White square on desktop after login

Hello I am a new Ubuntu user and am very excited about using the OS in place of Windows. Now to the problem I have a Dell XPS 400 tower and I installed a new hard drive and Ubuntu version 8.10 and it went through its general spill of install and was completed then I logged in using my username and password then it goes to the desktop for a second then goes to a black desktop with a white square in the middle of the desktop and if you try to switch between desktops it displays a triangle between desktops and I tried accessing the internet and the computer just freezes. So I put the ubuntu cd back in and ran the memory test from the cd it said that it found no faults then I checked the cd if it had any defects and it said the cd was fine. So this is where I am at. Any Help would be much appreciated thank you.:confused:

And some more info I am very new to Ubuntu and do not understand alot of the OS but am willing and wanting to learn thanks for understanding.:confused:

Try to run th Ubuntu from the live cd to see if you have hardware compatibility issues.Cause i had the same problem and i found out that the problem was my Graphics Card Drivers.Use Envy to install nvidia or ati drivers or use the restricted ones.

Hey thanks for the advice worked great it ended up being a driver for my graphics card like you said. I turned the graphics off them boom there was my desktop. Then installed the new driver then the problem was fixed so thanks again.:guitar: