no srsly though, can we have some feedback (error messages etc.)
If you are getting a kernel panic (absolutely nothing happening -- screen frozen etc, sometimes lights on keyboard flashing) it is probably a problem wiht hardware: try unplugging all usb devices and booting, and then pugging them back in one by one until you hit the one that was causing the error.
Have you checked your cd for defects? It might be that it is damaged/corrupted in some way, in which case you'd need to re-download/re-burn or order a free copy from ubuntu via ShipIt. Make sure your motherboard, chipset, graphics/sound card, drives etc are supported (just google their name with "linux" and have a look what comes up).