My laptop did the same when I powered it up a couple of days ago. I traced it, in the end, to wuauserv, the Windows Automatic Update. I killed that process, and the machine returned to normal.
There were about 50 updates waiting to be installed (all from within the past week), and I think they were just too many for the memory or the CPU. I updated "manually", doing them three or four at a time. It's now up to date again and running normally. Pain in the neck, though.
My desktop, witha faster processor and a lot more memory, seemed to have no problem.