It could also be a physical drive failure or memory issue. You can often go to your hard drive manufacturer's website and download a disk utility as a bootable .iso that you can burn to a cd and boot from to run hard disk diagnostics.
As for checking memory, download and burn this
http://www.memtest.org/download/4.20/memtest86+-4.20.iso.zip to a CD. Boot from the CD and let it run through the tests 3 times. There should be no errors found.
However, if it is one of the above, it doesn't mean that the Win7 installation won't require a complete reinstall, which it sounds like it does.