Hi
Try booting into safe mode (press F8 when the computer starts and select the option to start in Safe Mode), and then click Start>Run and type this:
scf /scannow
in the dialog box. This will start the System File Checker and make sure your system files are intact.
If that does not help solve the problem try running the CheckDisk utility: Right-click My Computer, select Manage, click Disk Management, right-click your boot drive (normally C), select Properties, then click the Tools tab, and click the Error Checking button. Click Check now and make sure that the options to check for and recover bad sectors and Automatically fix errors are ticked. The next time the computer is rebooted, chkdsk will run and check your drive.
If this does not work then you should run some diagnostics to make sure your registry is OK, and check for viruses as well.
Good luck