Okay, here goes. The instructions are based on Windows XP that is somewhat out of date. There are various ways to get to the part on your computer to uninstall then reinstall the driver for your monitor, but since I do not have all the current windows "security patches", I'm going to take a long but tried and true route. Also note, if there is any unfinished work like word documents that you are editing, emails you are composing, etc, finish them before proceding. At the end of this procedure, there is a good chance that your computer will need to be rebooted.  

Be aware that while this procedure is not really all that complicated, there are a number of steps and clicks involved, with some potential variables and or options that may appear for which I cannot predict ahead of time. For instance, after the monitor driver is uninstalled, the next step is to re-install this. Windows makes this pretty easy, but people who resell computers can complicate or outright remove this otherwise easy procedure. The best way they can complicate this step is by not having installed the computer to have copies of all the Windows driver files and CAB files somewhere on the computer. This will cause some headache when it comes time to reinstall the driver. See more below. The good news in this is that, as far as potential for really botching up your computer, diagnosing/uninstalling/reinstalling the monitor driver is a fairly limited risk. Perhaps you may want to read the instructions first to allow them to sink in, then perhaps take a dry run following all the steps one by one EXCEPT THE CRITICAL ONE as noted for you below. If the dry run turns up situations which I did not cover and this concerns you, just post another question to the forum with the details and I'll try to figure it out from there. In other words, try all the steps leading up to the critical one, but stop at the critical one. If you have questions or problems, just post them. If not, then go procede with the critical step.

First, open Control Panel. Depending on variables that may have been tweaked on any given Windows computer, this may be as easy as clicking on the Windows Start menu, then clicking on Control Panel, but how many clicks and where exactly you need to click may vary depending on how your computer was set up and later tweaked or customized for you own likes.

For instance, I'm an old schooler, I prefer to view things on my computer using the old fashioned List - Detailed View. More recently, Windows PCs have been shipping with a graphics view preset, this shows you pictures of all the entries in your Control Panel rather than words. Either way, you need to find the word or picture for Display.  Double click Display to see the Display menu, across the top of which will be various sub-menus ("tabs") to click on. Find the one called Settings and click it. The Settings menu allows you to look at the current settings for the display as well as make changes. While you are here, make a note (mental, or write it down) of the information shown near the center of the Settings window where you should see the Display: XXXXXXXXXXX For instance, mine indicates  Display: Plug and Play Monitor on NVIDIA GeForce4MX 420. BTW, this provides a little bit of info, from Windows perspective, about your Monitor and Video Adapter Card. Note that from Window's perspective, my monitor brand is "plug and play".... isn't that special? And the video card brand is "NVIDIA GeForce". The latter is actually usefull info. The former is sorta kinda useful info in that it doesn't really tell you the actual brand of monitor, but it does tell you that whatever brand it is, Windows generally knows that it's one of the many from the world of plugNplay.

In the bottom of the Settings menu, there is a tab for  Advanced; click Advanced. The Advanced menu appears and should contain various tabs, such as General, Adapter, Monitor, Troubleshoot, etc. Click on Monitor. Note that the Monitor menu shows a little bit of info, including monitor type - plug and play which we already knew from a previous menu.

Also make note of the few settings at the bottom of this menu: Screen Refresh Rate (mine is set to 60 Hz) and a little check box option (you may or may not have this) that indicates Hide Modes that this monitor cannot display.  For what it's worth, my check box is checked, meaning my computer is set to hide monitor modes that my monitor cannont display...... makes sense to me :)  Also note there is an option to Troubleshoot. Make note of this, if reloading the driver does not help any, you may want to give Windows a chance to troubleshoot to see if it can identify it's problem.

Now, finally, we are getting close to the Critical Step. Click the Properties box in Monitor menu. There are generally 2 menus here: General; Driver. Click on the Driver tab. You should see some general driver information here as well as various options to include Update Driver and Uninstall Driver.  This info should be headed by plug and play monitor and include info like driver provider, driver date, driver version. Write down this general information, then click Uninstall Driver. This will cause a prompt to inform you that Windows now knows that you are trying to delete your monitor driver and do you really want to do this?  THIS IS THE CRITICAL STEP. The ideal next step is to click Okay. However, if you have any unexpected problems or questions that have arisen, post them on the forum before proceeding with the step of clicking Okay.  

Your monitor driver is now uninstalled but your system may need to be rebooted in order for you system to really really acknowedlge that the monitor driver is uninstalled. So, reboot your computer. There are various ways to do this. An easy one is to click the Windows Start thingy, and select the option to Turn Off Computer. You don't really need to turn off the computer, you can if you want, but this is just an oddity in the way Windows decided to label the shutdown menu. After clicking on Turn Off Computer, a menu should appear to give you a choice of shutdown to include Restart and TurnOff. Choose Restart. This will cause what is known as a warm reboot .which starts with the computer shutting down but then starting right back up again. Once your computer begins to start back up, it may delay a little longer than usual. At some point, depending on other variables, Windows should display a prompt message  that indicates something to the effect of "hey, you, the fancy Windows plugNplay wizard has detected that you do not have any monitor driver installed.....would you like windows to install a monitor driver?". Click Yes/Okay to install a monitor driver. If windows prompts and asks "where do you want me to get the driver" it will generally give two options:  automatically find driver ; install from a specific list or location. Choose the option for automatic. This will cause windows to find the appropriate plugNplay monitor driver from the copies of such driver files and CAB files that should have been created when the PC was built and Windows installed. It's difficult to guarantee that evey computer reseller follows this procedure. If by chance your's did not, you may be able to get around this small problem in one of two ways: 1) you may have gotten a whole bunch of diskettes and CDs when you bought this computer. You may have put all this stuff into a box you labeled "a whole bunch of stuff that came with my computer that I don't know what to do with"  If so, check this box to see if you can find a diskette or CD that has your monitor driver file on it. Another option is to go to the web site of the monitor manufacturer and download the driver from there. This will require you to know the brand and specifici model number and or model name of your monitor. This info can generally be found imprinted on a tag somewhere right on the monitor.

So, how lucky are you feelilng? Don't worry, even if things go as bad as they possibly can with the monitor driver, Windows realized a long time ago that it's very critical for Windows OS to be able to boot even when there is a problem with the software used for the monitor driver. For this reason, Windows has a way that I've yet to see fail that allows it to boot, and which allows any monitor to work in a basic mode so the user can watch and observe the boot process. Any questions or problems, just ask. 

Good luck. 

PS - since this was a somewhat invovled post, it may take me a while to get it posted to the forum AND THEN go back and check for major spelling or other errors that I'll need to fix and re-edit.

End of take 1