First of all, try to perform an in-place upgrade installation to repair a flaky existing install. This process involves multiple stages, like copying installation files and gathering existing files and settings. This procedure is not possible if you system cannot boot to the Windows desktop.
Another similar way to repair is ‘System File Checker’. Click on ‘Start’ menu, and run "sfc /scannow" (without quotes but with the space). Be patient, because this may take several minutes.
‘System Restore’ is another important option. You will find this option in the ‘Start’ menu, and it takes you back to an earlier working version of the Windows. Remember, this will remove all your recently-installed programs.
If none of the aforementioned options works, go for a repair installation. But remember, it must be your last option. And this should be done only after removing spyware from your system, reinstalling your drivers, and unsuccessfully trying ‘System Restore’.
Before going for a repair installation, you need to take a few precautionary measures. First of all, transfer all your personal data to an external drive. Backing up your data is very important.
Uninstall all antivirus programs, which you can reinstall after completing the repair process. Delete the temporary files in your computer. Don’t forget to remove the hidden files.
You can unhide the files by using ‘Folder Options’. Clean up the entire system before going for a repair installation, for which you need a Windows DVD.