My LCD ViewSonic monitor keeps flashing, help!?

Basically, my computer has a few problems, it kept saying that CONFIG/SYS was corrupt on boot up, I reformat, and a sied efect seems to be the monitor flashing and the computer running slowly, but I have had to reformat three times this week (Im using xp). Its not the monitor, because it only flashes when I use higher drain applications. Please tell me whats wrong with it and how can I fix it, also, please can you give me some suggestions as to why it keeps sayin config sys is corrup, ive never had a virus or anything!!! Thanks!