[Irrintra]

I received an HP Vectra VL420 that doesn’t properly boot; there is no video output, and I’m pretty sure the monitor isn’t the problem; it acknoledges being plugged into the VGA port, but doesn't do anything when the computer is booting, can't see the BIOS.
I can turn the computer on and see the PC's power light illuminate. The activity light also turns on, but after a bit, it dims. I can hear the fans spinning inside. I tried removing the RAM, but the computer doesn’t issue any beep codes, so the computer’s not POSTing. I’ve also tried swapping graphics cards to no avail.
I plan on swapping out RAM and graphics cards just in case the ones I tested with were bad. What else might be the problem?

[dustyjay]

The problem could the power supply. Just because fans spin and lights flash, even cd drawers open and close does not mean the power supply is providing the proper power for the rest of the system to run. The computer not posting is also an indication of a possible power supply problem. It could be other things, such as a bad motherboard, but the power supply is usually the easiest to check first. All you have to do is connect a known good power supply, (New does not mean known good, known good is a power supply that in known to be operating in a working system) to the motherboard then see if the system will operate. If it does you have found the problem, if it does not you have eliminated the power supply from the list of possible problems.