Hi UNTAMED,
I do not see how a registry defragger could do this either. It sounds like McAfee may be blocking something or having problems of it's own as SIW2 suggested. You might consider uninstalling McAfee just as a test to see how your system runs without it.
If you still need to fix your system, then you might try doing a System Restore (Method Two below) using a restore point dated before the problem.
System Restore - How to
Hope this helps,
Shawn