White screen on W98

I have a Compaq Presario laptop with Windows 98 fitted as
OEM. Computer works OK but after a while, which may be
short or long, depending on its mood, the screen just
blanks out while the programmes continue to run in
background. I then have to shut and restart a few times
until I can have a new PC session. Compaq, predictably
enough, says their laptop is fine but that there may be a
problem with the software. Since the screen works well
when it wants to, I dont see a connection problem and I
checked for worms and viruses so I am at a loss to
explain?

Please reply to