If your system starts behaving strangely, it may be that one or more of your registry hives is corrupt. One way to check for this is to examine your event logs for event ID 6008, which indicates an unexpected shutdown of the computer took place. The problem here is that when a computer shuts down unexpectedly, for example in the event of a power outage, and the computer was modifying the registry at the moment the outage occurred, then a registry hive could have been placed into an inconsistent state. When the computer starts back up again, the operating system has difficulty loading the hive and erratic system behavior results. If the hive corruption is serious, you may even get a startup message saying Windows couldn't start because a file is missing or corrupt.
Motto: check your event logs first when things go wrong and look for clues to help you troubleshoot your situation.
Mitch Tulloch is President of MTIT Enterprises, an IT content development company based in Winnipeg, Canada. Prior to starting his own company in 1998, Mitch worked as a Microsoft Certified Trainer (MCT) for Productivity Point International. Mitch is a widely recognized expert on Windows administration, networking and security and has written 14 books and over a hundred articles on various topics. He has been repeatedly awarded Most Valuable Professional (MVP) status by Microsoft for his outstanding contributions in supporting users who deploy Microsoft platforms, products and solutions. Mitch is also a professor at Jones International University (JIU) where he teaches graduate-level courses in Information Security Management (ISM) for their Masters of Business Administration (MBA) program. For more information see http://www.mtit.com.