If this is a Windows permission error, i can only think of the windows installer cleanup tool which cybercore mentioned, but it really depends on a system recovery.
That's all I can think of right now since system restore doesn't work and windows installer is messed up.
Wait, I just got an idea.
Search the internet for TuneUp Utilities
Download and run the program
under performance, click fix issues
dig around; there should be something about fixing Windows Installer.
I am in no way affiliated with TuneUp Utilities.
NOTE: System Recovery should be used as a LAST resort to fix your problems.
it wipes all of your information off the hard drive.