Windows 7 Train wreck

I have a computer running windows 7 that I purchased online (no windows disk). I get a message saying "This copy of windows is not genuine" Tried to activate in control panel. No good. Tried to activate with slui.exe 4 command. No go . Tried to make a repair disk but it doesn't do anything. When I try to do a backup it fails and says I have corrupted files on drive C. The computer sometimes freezes when booting but once running performs fine.I also purchased a windows 64 repair disk on line but that also doesn't work. I would like to get the computer running clean without losing all my data

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