Cannot run cmd or regedit

Sounds like something needs repairing.  Try typing in 'sfc /checknow' into the Run box (requires the Win CD) to repair some system files.

Yeah...  I tried an inplace repair.  You get to a point where you enter the key and  then several minutes later a portion of the repair starts over and you're entering the key again.  Endless loop.
Ran sfc to no avail.
Can't boot to a PE CD... not enough RAM.

Bugger.  The lack of RAM for PE sounds odd.
Have you looked through the Event Logs.  You should be able to see some errors or codes that can lead you on a path of googling to see what is causing the mini-crashing.

Could also mean malware infection, some malware will disable regedit,CMD,Task manager,etc..
Downoad Malwarebytes anti-malware, Install, update & run a full scan.
also showing us a hijack this log can help.
finally it may also be a good idea to run an online scan at Kaspersky Online , Please post back any logs .

Thanks!

We also had this issue and this was the resolution - Thank you!