infinite loop on (Step 3 of 3) in boot cycle

I purchased the registry repair tool and ran the clean up memory problems option.

It went through some changes and was set to auto restart after repair. That was the last time I was able to run windows with my computer.

When it is at the "step 3 of 3) it is not allowing any access to the computer (ctrl-alt-del does not work). Then it cycles again for another reboot - only to be in the same situation.

If I do a hard power down, it will restart to the options of "start windows normally" or the recommended "repair and diagnosis" options.
I ran the "Startup repair" and it gives the "Unspecified changes to system configuration might have caused the problem" with a Repair action: "System files integrity check and repair"

How do I do the integrity check on the system files?

Please advise...

Welcome
For now and the future do not use tamper with registry unless you are quite knowledgable. To try to fix this problem, try to get to system restore in safe mode.
http://www.vistax64.com/tutorials/76905-system-restore-how.html

I had that happen once after an update. Follow these steps: Latest Vista Update stuck in Stage 3/restart loop - Microsoft Answers

Also don't mess with the registry or use registry cleaners, optimizers, etc.