|This will happen for one of the following reasons...|
- Installed a Bad Driver -> To fix, F8 boot and select last known good configuration.
- Bad or lost system files. -> To fix, boot from the System Disk that came with the computer and do a repair install.
- Failing hard drive. -> To fix, boot from the System Disk that came with the computer and go to Recovery Console. Then run the following command
CHKDSK C: /F
My guess is your problem is the second problem. You may have gotten a virus that hosed your system files while you were browsing. To fix this boot from the system disk that came with your computer and do a repair install.