Here's basically what you need to do as a starting step.
- Boot the computer using installation media (Windows Operating system disk)
- Attempt to repair the issues in the preinstallation environment
First off, if you do not have a windows 7 installation disk, you can
download it from microsoft.
Download the correct version for your system and burn it onto a DVD using another computer.
To boot from the DVD drive you have to instruct your system to load from the DVD instead of the hard disk. Usually this is done by hitting a key on the BIOS loading screen. Here's an example,
if this was your computer, you'd hit the ESC key. But depending on your computer, can be be F9, F10, F11, F12, whatever. The BIOS screen should tell you what key stroke changes the order. He's an image from a Virtual Machine. It says ESC for Boot menu. You need the boot menu.
When you have it, select the DVD drive to boot from.Here's an example from bleeping computers that shows you how to get to the command prompt. This is where you need to be to run a tool that may fix your problem.
http://www.bleepingcomputer.com/tutorials/windows-7-recovery-environment-command-prompt/
When you get to the command prompt, type the following command
chkdsk c: /r
This tool will check your drive for errors. If it's just a few bad sectors preventing your system from loading or if some pointers are broken, then it will fix it. This tool does take some time to finish so check back every 10-15 mins.
Once it's done, reboot the computer and cross your fingers.