Black screen after boot

Guys I really want to use ubuntu but i have a big problem. i've successfully downloaded and installed ubuntu on my pc (desktop edition). Then after installing, i restarted my pc. The logo appears during boot and also the sound but then after that my screen went black. my mouse pointer is moving though but nothing happens. Need help please.

Make sure you don't have

Make sure you don't have anything else connected to the computer while booting.  I had a similar problem with a family computer which had an iPod connected.  The computer was then trying to boot from the USB connected iPod.I doubt this is your problem, exactly, but you may have your boot order set incorrectly in bios.  Make sure you are booting from the HD first.  If it's trying to boot from the CD or USB first, you might see the same problem I saw with the iPod.Good luck.