Resolution resetting to 1280x760/1024 after PC reboot/reset.

Hi, just wondering if anyone could help me with this problem. Upon restarting my computer, 50% of the time it will load all the icons, DELL's centre program pops up etc along with Zonealarm and then suddenly the resolution will change from the wanted 1680x1050 down to anywhere from 1280x720 up to 1280x1024.
As far as I can remember this has only started happening ever since I played the Final Fantasy 7 demo, I accidentally hit the windows key and the entire computer pretty much froze, had to pull the plug in order to restart.

I've tried registry cleaning but no use.
Any ideas?