Monitor turning solid white

while on internet and sometimes while not on the internet. Sometimes the screen turns white with blue lines straight up and down. Does anybody know whats causing this. My computer is only 16 months old. HP windows xp. When it does this, I cannot turn off the computer with the start button. I have to turn it off using the tower off and on button. Is this a display problem or a motherboard problem? Ive called HP tech help and they said I need a brand new computer. They offered to sell me a new one. They happen to be having a sale on them this week, Sounds fishy to me. I also called one of those computer repair companys in my city and they didnt know what the problem could be. They also said they have new/used ones they could sale to me. Ive run all the tests for my system and they all said (no problems found). Somebody out there must know something. I cant be the only one with thats ever had this problem. Any help would be appreciated.! Tweet