Hi,
Did you make any changes on the computer prior to the issue?
Method 1:
Run the fix it and check.
Fix Windows system performance problems on slow Windows computers
http://support.microsoft.com/mats/slow\_windows\_performance/en-us
Method 2:
Perform a clean boot and check if any third party software is causing the issue.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
http://support.microsoft.com/kb/929135
Note: After trouble shooting put the computer to start as usual by performing step 7 from the above Knowledge Base article.
Method 3:
You may diagnosing memory problems on the computer
by following the steps from the link.
http://windows.microsoft.com/en-US/windows7/Diagnosing-memory-problems-on-your-computer
Method 4:
Run a Microsoft safety scanner to make sure computer is free from virus infection:
http://www.microsoft.com/security/scanner/en-us/default.aspx
Disclaimer:
If you run the virus scan the program that is infected with virus will get deleted. So you have to reinstall the program. Also if the files and folders are affected with virus then they might even get deleted
Method 5:
If the above steps doesn't help then you may run chkdsk from WinRE(Windows Recovery Environment )mode and check for the issue.
Refer the following link to obtain more information about system recovery options.
What are the system recovery options in Windows 7? ****http://windows.microsoft.com/en-US/windows7/What-are-the-system-recovery-options-in-Windows-7
Refer section: To open the System Recovery Options menu on your computerto enter System Recovery Options
Select the Command Prompt option. At the command prompt, type the following command, and then press ENTER:
chkdsk drive: /r **** chkdsk drive: /f **** Chkdsk disclaimer: ****Important: While performing chkdsk on the hard drive if any bad sectors are found on the hard drive when chkdsk tries to repair that sector if any data available on that might be lost.
Post back the results.
Reference links:
Ways to improve your computer's performance
http://windows.microsoft.com/en-us/windows7/Ways-to-improve-your-computers-performance
Optimize Windows 7 for better performance
http://windows.microsoft.com/en-US/windows7/Optimize-Windows-7-for-better-performance
Post back the results.