Try running scanreg /restore from a bootdisk Xeno-Fenix.
If you dont have a bootdisk, you will need access to another PC. Go
here and download a bootdisk file to the PC. Put a formatted floppy disk in in the drive and doubleclick on the file to create the bootdisk (follow the prompts). Next, powerup your PC with the bootdisk in the drive.
At the command prompt A:\> type:
c:
Press Enter then type:
cd windows\command
Press Enter then type:
scanreg /restore (note the space after scanreg)
Press Enter
Follow the directions (remove boot disk first). You should be able to choose from a "started registry" using your arrow keys. Select a date when you know that the computer was running well from the first 4 (I dont think the 5th one works). When you have finished type "exit" (no inverted commas) and with a bit of luck, Windows will load.
The links to any software or hardware installed after that date will be lost so you will have to reinstall it.