Windows 98′ hangs at system shutdown

I was on the Microsoft website and they recommended certain upgrades to my Windows 98′ system. I downloaded 3; 1)called “critical” to improve internet security, 2) a “critical update” monitor to let me know when updates are available, and 3) Media Player 7. My system would not boot into windows after installation. I uninstalled critical update monitor (no help) then Media Player 7. System seems to be OK now, but hangs at system shutdown. Will not CTRL+ALT+DEL reboot; must power down. Norton WinDoctor finds no problems. Have to power down to unhang. Computer is a Compaq 5875 650mHz Athalon. Any ideas for a solution?