Start Up Cannot Repair

I bought a ZT Systems computer about a year ago. It came pre-installed with Vista. After numerous crashes down to the black screen, I was told that Windows 7 was a more stable OS. We did a clean install, and all was well for about a month. Then another black screen crash. Reinstalled, and another crash. Did custom install yesterday. Was running long enough to run a registry cleaner and install antivirus software. Crashed during antivirus scan. Now I am stuck in an endless repair loop. I allowed the system to complete each repair cycle, regardless of how long it took. If I can get to the desktop, it will just crash, then back into the loop. I receive messages indicating startup repair cannot fix the problem. Computer says there are no restore points. Now, the repair loop does not recognize keyboard prompts, so I cannot try to reinstall again. Help?