Hi,
The only thing you can try is a full (erasure) of your current hard drive and see what happens if you try and reload W7.
Try this at your own risk. You will lose all files and programs. I pretty much guess you have lost them anyway...
Here is the info about the free utility, and what it does.
The first download will make a bootable CD for you.
If that doesn't clear the problem and you still can't install W7, I would imagine you need to get a new hard drive.