Why will my computer not boot up?

[mamabearlongs]

I have a Windows XP desktop computer that stopped will not boot up completely. When I turn it on, it does not go past the first screen which is the screen with the word Dell on it. If I unplug it for ten seconds and turn it on, I will get a screen that looks like an MS-DOS screen that says something like, the computer has failed to boot up. I would appreciate some advice on how to fix this problem. The manufacturer of this computer is Dell.