A problem in Windows Automatic Update has been causing slow-running, high CPU load, and overfilled RAM since -XP days ( and still today in Win-7 Home Premium, 64-bit). Turn on the Task Manager with a control-shift-Escape and see if the CPU is full (100%) even while nothing else is running. Also look at the memory usage and see if it is above half of all installed memory. Click the 'Resource Monitor...' button and look for "svchost.exe(something)" at the top of the list & showing excess CPU use. Luckily the answer is simple: turn OFF Automatic Updates --- click Start, Control Panel, System & Security, Windows Update/Turn automatic updating on or off. You can always go through the same path to Windows Update and do a manual search for updates anytime that is desired.
Good luck!
a r t