I use to have the same problem. I narrowed it down to a 3D graphics conflict between a 3D Screensaver I was using and my ATI Graphics card. Computer got stuck in an “loop”, like the two processes were waiting for the other to respond before engaging.
To maybe get some info, try this:
Right click: My Computer
Left click: Manage
Left click: the ‘+’ sign
Left click: ACEEventlog; Application; etc...
Search for: Any Yellow Warnings or Red X signs.
Left click (possibly double click) to open the event
This should give you some info with possibly a link for more info.
That’s how I tracked my problem.
Hope this helps.
a.k.a. - a deadlock condition.