Try restoring the registry:
Boot up the computer, then after 'Press Del to entre BIOS' option on the screen, keep pressing F8 repeatedly until instead of loading Windows it will go to a six option DOS menue screen.
Scroll down, using the arrow keys, to the option 'Command promt only' then type SCANREG/RESTORE and enter.
After the computer has scanned the registry you are now presented with a list of the last five days when the computer booted correctly. Select a date just before the computer went pear-shaped and ask it to restore the date selected.
Give that a try.