Sort the processes tab in task manager on the cpu column and see if some process is spiking. If not, try a clean boot and work backwards (Open msconfig and on the General tab choose "selective startup" (disable everything from loading) and reboot. Does the problem still occur? If not, start adding items back to msconfig one or two at a time, rebooting after each change, until the problem reappears and you'll have identified the offending process. This is clearly a time consuming process, but it is the best way to determine if some process loading with the system is the cause of your problem.)
