Perhaps you have multiple Antivirus systems installed on your hard drive? That could be a possible reason for doin' this.
Do you have any programs which could possibly damage the system files of Windows?
Anyways, try to log in in Safe Mode (press the F8 key at startup a few times and choose "Safe Mode"), and uninstall every program which most likely can cause the error. If you've installed something recently, that may be the cause of this error.
You may also give a try restoring the last known good configurations. Start to hit F8 at startup, and choose "Restore latest working configurations" or something like that. This usually fails, but you may give it a try nonetheless.
If none of these have worked, or y'can't even log in in Safe Mode, y'should take out your hard drive, and connect it to another computer, where y'have the opportunity to save all your valuable data to discs or anywhere they're welcomed. Then do a format C: on your hard drive and reinstall Windows. Drastic solution, but it works in 90% of most cases.
If it still not works, you possibly have a hardware error. Check the motherboard battery, the condensers and the power supply.