Vista - Problem with unwanted zooming in

I have a recurring problem with windows vista on my dell inspiron laptop.
Every so often when I try to adjust the brightness of my monitor using the
function and arrow keys it won't work. After a few attempts something quite
strange happens - everything starts becoming larger as if I'm zooming in on
icons and text.
Everytime I open a new window the text starts off normal size then increases
in size to a ridiculous extent so the laptop is effectively unusable. The
only way to solve it seems to be running system restore and then waiting
until it happens again.
Do I have virus or is there a fault with windows vista or dell's hotkey
setup?

Thanks

Hi Chris,

It sounds like you accidentally activated the Magnifier feature in Vista. Check these settings to turn it off:
1. Open Control Panel (Classic View)
2. Click Ease of Access Center.
3. Click "Make the computer easier to see"
4. Uncheck "Turn on Magnifier"
5. Click Save.

Shawn