O/T Computer issue question?

Sorry for posting here but I know some of you guys better than others on other forums. Since you use computers lol thought you might know the answer.

Had a trojen (sp?) a few months back...had to take the computer to have it cleaned and restored. Doing fine for a while then the last couple of days I keep picking up another trojen.

I've run malwarebytes (which was installed at the time of cleaning & restoring) which is suppose to be one of the best and it was picking them up and getting rid of them, the last couple of days.

Now all of a sudden it's not picking it up. I know I have another one though because of the way the computer is behaving. Exp: I google something and click on a reliable link and the info on the link is rerouted to an advertisement.

So...any ideas (other than taking it back to the computer shop)to find/clear this bugger?

Thanks