Hello shoaib khayana and welcome to Seven Forums.
It would help to know what your system specs are. At the top of any Forum page click on "User CP". Then in the left column click on "Edit System Spec" and fill in as much information as possible. A free program called Speccy can give you the info. Speccy - System Information - Free Download
It sounds like you might be trying to do a Repair Install. If so, see if this tutorial can help. Repair Install
Another option, and perhaps something to try before
a Repair Install, is to run a system file checker scan from an elevated command prompt (option two, this tutorial.) If any problems are found run the scan 3 times, rebooting in between each scan. SFC /SCANNOW Command - System File Checker