I'd start by running
scanreg/restore from the DOS command prompt. Choose a date prior to the beginning of the problem. Reboot. If this doesn't work, you can do a "dirty" or "over the top" reinstall. You will need your original CD and and product key. This will reinstall windows without loosing all your data, although some changes/updates may revert to their original files, as this is what windows attempts to do (can you say, IE4?
) You may wish to retrieve your product key first, for safeties sake.
From the start menu, select "Command prompt only". Type this from a DOS prompt only
(NOT start/run).Find.exe/I "ProductKey" %winbootdir%\SYSTEM.DAT Carefully note and write down the product key. Restart and allow windows to proceed with the installation
-----with one notable exception------. Windows will try to install to a secondary directory with a name similar c:\windowsII or other off the wall name. Choose the original windows directory. Provided there are no other major malfunctions, You should should wind up with an original windows installation, data intact.