CD IS NOT STARTING OR INSTALLING UBUNTU!

After successfuly downloading and burning the image of Ubuntu 7.04, 3 of my PCs with 256MB RAM, 880Mgz and 20MB HDD are not responding after I press enter on the "Start or Install Ubuntu" prompt. What could the matter be? Is it my Hardware? And if so, do I upgrade it (expensive) or do I use a lower version of the OS? Help???

possible bad download ?

I had the exact same problem. Tried it on both of my PC's and same thing. I assumed it was a bad corrupt CD and re-downloaded it and it then worked fine. Might give that a try. Other than that I know absolutely nothing about this OS :)