When I turn on my computer, the power light turns on, and I can hear it starting up like normal; but the monitor, keyboard, and mouse make no response. By this I mean, nothing is displayed on the monitor, the laser mouse doesn't turn on, and the lights on the keyboard don't turn on. I've tried switching the monitor keyboard and mouse with others, so they're not the problem.

Also, when I turn it off, the power light (on the computer) stays on. What could be causing this? This happened with no warning, and no major software changes were made before the problem occurred.

System Specs
MB: Pc Chips A11g V1.0
VGA: NVIDIA GeForce 6100
CPU: AMD Athlon(tm) 64 Processor 3800+, MMX, 3DNow, ~2.4GHz
OS: Windows XP
Memory: 1GB Kingston

it sounds like you motherboard isn't posting, i had a similar problem a few weeks ago and it turned out to be blown capacitors in the cpu power supply circuit. if you have a dvm or a power supply tester you should check you psu first, but it's likely that your motherboard has gone.

when you power on check if the keyboard led's will light up, if it doesn't then it could be a dying mobo.. or try using another a psu the easy alternative

I'm having a imilar issue. I'll be playing a game, then my comp freezes and I have to force shutdown. After it turns on, but no display, no bios load up, nothing. After some time it'll boot and say it failed last boot, and I hit f1 and it's working again. This happened after I changed a hard drive out >.<