The blue screen of death (BSoD) is often caused by a faulty video driver, it's the most common cause by far.
In safe mode, try to reinstall your video drivers.
If you can't reinstall the drivers in safe mode, You can try repairing, updating or uninstalling your actual video drivers.
Right-click the desktop and chose "Properties"
Sellect the "Parameters" tab and the "Advance" button.
In the new window, sellect the "Card" tab and the "Properties" button. A new window opens.
Sellect the "Drivers" tab.
Try the "Update driver" button.
You may also try the "revert to previous version" button.
It it still don't work, use the "Uninstall" button.
Close all windows and reboot when asked.
Once it's done, Windows will default to a basic generic CGA driver and display mode: Low resolution and only 16 colours.
You should now be able to start normaly, except that your resolution and colour palette will be 640 by 480, 16 colours. (Vista and Windows 7 will have somewhat higher defaults)
If it don't work, try to create a new acount and install from it. You can delete that acount later if you want to.
If you have more than one restore points available, try another one, it may just work.
Reinstalling Windows should only be attempted AFTER this, and only if nothing else works.
BEFORE you even thing about reinstalling Windows, be sure that you back-up all your datas and saved files. The reinstallation will very probably destroy most data on your hard drive.
If you have a second drive or partition, you don't have to wory about anything on that drive or partition.