This can be caused by a corrupt Windows file, and there could be several causes of that, from software conflicts to malware.
Let's see how bad the corruption is. Can you boot into safe mode and do things work in safe mode ok?
Hit F8 key repeatedly at boot up and make the proper choice when a list presents itself.
Then you could also choose Last Known Good Configuration from that list and see if that cures your ills.
Another thing to try is to boot to safe mode, and try to use the System Restore function. More info on this can be found HERE
If the computer won't start in safe mode, there is still a chance it will start in Safe Mode w/a command prompt. You can run system restore from there. Restart your computer, and then press F8
during the initial startup to start your computer in Safe Mode with a command prompt
. Then follow the instructions found HERE
Do you have your restore disks for this computer? (I am not suggesting to wipe everything out and start over - yet - but if none of these ideas work then we might try to repair the damage another way).