Start your machine with a boot disk to a DOS prompt. At the prompt, type the command;
(note the space between the g and /)
Scanreg will scan the registry and give you five previous dates that known good registries were saved by the system. These appear in the US date format mm/dd/yyyy. Choose a date when you know the system was running OK and select restore. The program will re-set your system back to that point in time, and you will loose any programs that have been loaded since (which could be the cause of the problem), but you will not loose any saved files, so your personal files should remain as secure as a computer ever is.
However, as we all know (and do!!!), backup important files just in case!.