Hi,
- Have you made any recent changes to the computer prior to the issue?
- Are you able to login to your desktop?
If yes check if your Windows is activated? To check that, follow the article
http://windows.microsoft.com/en-US/windows7/How-can-I-tell-if-Windows-7-is-activated
If your Windows is activated and still your desktop appears blank follow the steps below:
How to use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7
http://support.microsoft.com/kb/929833
Else if you are unable to login to desktop follow the methods below
Method 1:
Windows Vista or Windows 7 no longer starts, and the Startup Repair tool does not fix the problem
http://support.microsoft.com/kb/934540
Method 2:
Use the Windows Recovery Environment (WinRE) to run System Restore
a. Insert the Windows 7 installation disc into the disc drive, and then start the computer.
b. Press a key when the message indicating "Press any key to boot from CD or DVD …". appears.
c. Select a language, a time and currency, and a keyboard or input method, and then click Next.
d. Click Repair your computer.
e. In the System Recovery Options dialog box, choose the drive of your Windows installation and click Next
f. At the System Recovery Options Dialog Box, click on System Restore.
g. Follow the System Restore Wizard instruction as usual and choose the appropriate restore point.
h. Click Finish to restore the system.
To know more about “System Restore” visit the following link:
http://windows.microsoft.com/en-us/windows7/System-Restore-frequently-asked-questions