Why would Windows 98 restarts automatically when you use the Internet MSN Messenger MS Outlook and Explorer?

Restarts "Windows is shutting down..." or restarts like someone hit the reset switch? If it is the former, you have a process running in the background, perhaps with a timer or triggered by a certain action. Press Ctrl-Alt-Del and hit End Task until all you have running is explorer. Open Messenger, Outlook, IE, etc. one by one and allow them to run for a while. DO NOT START THEM ALL AT ONCE. This is most unmethodical and will reveal nothing. If Windows starts shutting down, one of those programs is infected by a virus/spyware. Internet Explorer and Outlook are notorious for exploitable software bugs. If it is the latter, chances are pretty good that your power supply is going south. Have you added any hardware lately? The newer high speed hard drives and video cards require more power than their older counterparts. Adding a new video card, hard drive, network card, Firewire card, etc. could put your computer's power requirements beyond the power supply's ability. I would recommend taking your PC to a professional. If you are so inclined, your power supply rating is located on a label on the power supply unit. When you go to the store to get a new PSU, make sure you're getting one with more wattage output than the previous one.