Work through the steps for Troubleshooting Windows 7 Failure to Start. You will need the Win7 disk System Recovery Options or System Repair Disk for repairs, which you can make on another PC of the same 32- or 64-bit version.

These lead up to if necessary rescuiing your files to run Factory Recovery from its hot key at boot, or doing the superior Clean Reinstall Windows 7. It discusses in Step 1 how to find reinstallation media. We can help you.