Try booting the computer in Last Know Good Configuration. Turn off the computer by unplugging it or using the "kill" switch in the back. Wait 30 seconds and turn on the computer. Start to hit the F8 key to enter the boot menu. If this does not work then reboot and hit the F2 key. One of these keys will usually enter the boot menu. Which one depends on the BIOS you have. When the boot menu comes up, pick Last Know Good Configuration and hit the keyboard's Enter key.
If it does not work then go back to the boot menu and pick Safe Mode. Wait a long time (about 180 seconds) for the desktop to come up in Safe Mode.
Now in Windows XP you can go to the Start button on the lower left, click on Run, and type in msconfig. The Systems Configuration screen will pop up. Under the General tab about dead center at the bottom of the box you will see Launch System Restore. NOT SO in Windows Vista.
In Windows Vista, click on the Start button and type System Restore in the Search box. Either way, a System Restore box will open with a recommendation by Windows on a restore date. Ignore that and Choose A Different Restore Point. At the next window check the Show Restore Points Older Than 5 Days and pick a date at least 2 weeks old or BEFORE the time you first began to notice this problem. Click next and follow the prompts. When the computer reboots back to your desktop and everything seems ok, run a good antivirus software immediately.
This should fix your problem. GOOD LUCK
If it does not work then go back to the boot menu and pick Safe Mode. Wait a long time (about 180 seconds) for the desktop to come up in Safe Mode.
Now in Windows XP you can go to the Start button on the lower left, click on Run, and type in msconfig. The Systems Configuration screen will pop up. Under the General tab about dead center at the bottom of the box you will see Launch System Restore. NOT SO in Windows Vista.
In Windows Vista, click on the Start button and type System Restore in the Search box. Either way, a System Restore box will open with a recommendation by Windows on a restore date. Ignore that and Choose A Different Restore Point. At the next window check the Show Restore Points Older Than 5 Days and pick a date at least 2 weeks old or BEFORE the time you first began to notice this problem. Click next and follow the prompts. When the computer reboots back to your desktop and everything seems ok, run a good antivirus software immediately.
This should fix your problem. GOOD LUCK