Computer won't start up, HELP appreciated.

My computer won't start up, it gets to a black screen with a blinking underscore in the top left, then just stays there. I can't enter safe mode or anything, since it doesn't start up.

The computer is running Windows XP.

It only had a little less than 10 GB memory left, but I think it should still be enough to run the system. May have something to do with the lack of memory, but I don't know and there's no way for me start up the computer to find out the problem.

All help will be greatly appreciated!

What kind of computer is it? Like a hp, compaq, dell, or any others. Have you tried to run a hard drive test that most makers have built into the bios? Also was the computer running slow or throwing up errors before you couldn't boot up completely?

Is your CPU activity light on, if not then your CPU is off, which means the power to the CPU is not plugged in(maybe a cable slipped) or your CPU is Fried. Also check the Powersupply is connected to your HDD.

Well since its getting to the prompt screen for windows its posting fine and if it was the power supply it wouldn't boot properly like saying that it couldn't find the boot sector. I wish the op would post more information on this matter so we can find the answer for him/her.