Reset screen resolution

This solution is ugly, but should work:

• Boot in safe mode (via F8)
• Remove the driver for the graphical card.
• Reboot. Win7 will revert to the default driver which only supports 640x480 and 800x600. I think 800x600 is the default for this one)
• Happily log in and reinstall the driver.

Solutions which I think are much better but which require additional hardware:

• Connect another monitor which works with the current resolution
• RDP (if enabled) from another computer, which uses that other computers monitor and resolution.

Try booting into Safe Mode by pressing F8 before Windows starts loading. Then you will be able to change resolution and reboot computer alter to see if change took place. Otherwise there is Safe Mode with step-by-step confirmation that you can try.