Using Windows XP - and IBM Client Access. After setting up initial client access sessions, another user logged on to the computer and tried to start up sessions. It gave an error, and now the CPU usage is 100% - even after uninstalling Client Access and with no other programs running.
Open your task manager and see which processes are using the time, by percentage. This can point you to the culprit, which may be a desireable program or spyware or worse. Beware of arbitrarily ending processes, though, unless you know what they are. Do a google search for any you don't recognize. I know my system has problems with a proprietary invoicing program that makes poor use of MSAccess... I find Access using near 100% while that program is idle; sometimes restoring the program brings he time down. This lame program crashes Access several times a day, usually when cashing out a customer. Lesson learned: Demoing a POS system with a small test data set doesn't uncover problems that arise when you have committed to massive data entry. Another problem is Acrobat got corrupted at some point, and if I click on an unlabeled PDF link, I have to close it in task manager or it uses 100% processor cycles without opening. More common is spyware or other malware. Best to run a good spyware and virus program while you are at it.