Computer help: page keeps moving up / down

page keeps moving up / down

My problem is, when I am typing or reading web pages,the page I am on keeps dissapearing up the screen. Typing is the worst, because when this happens, I end up typing somewhere I do not want, like typing in middle of other written lines. I keep my system clean, no viruses, so reason unknown.

Any advice on how to fix would be appreciated.

I have windows vista home premium.
13.3'' widescreen TFT
120gb HD
optical drive-DVD+/- RW
I have about 1gb memory

E-System Laptop 1412

This problem is annoying to say the least.

Thankyou for your time.