While my PC was powering up, everything shut off as if it had been turned off (complete shut down). When I tried to restart it, only the fans (two case fans, CPU fan and graphics card fan) and cathode light tube would come on. The light tube would only come on about half as bright as normal, and only along about 3/4 of its length. The green and amber lights on the front of the case stay steady, but there is no hard drive activity, and no activity from my power supply (none of its fans running), monitor, keyboard, etc. No startup test beep is heard. While troubleshooting, I disconnected all the power inputs to the motherboard, optical drives and disk drives to test the power supply (Allied 400W). When the tester was switched on, the power supply's fans ran along with the case fans, CPU fan and cathode light as described above and I got the green light on the tester indicating that the power supply is OK. When everything was hooked back up, the power supply would have no visible activity, but the rest of the fans and cathode light came on again as described above. No hardware changes have been made since a memory upgrade about a month ago, and I'm running XP Home, P4 2.8GHz, 1.5 GB RAM (3 banks of 512MB Crucial), and an MSI 648 Max MS-6585 ATX Mainboard. My system is about 21 months old, but the motherboard and CPU are only 14 months old. Any thoughts or suggestions? Thanks.