ubun2^beta

I upgraded to Ubuntu 10.04 and now my computer won't start. At first it did but after the last restart it did not boot. It does not show any boot menus or anything. How do I go about booting it from a CD? What do I do afterwards? Thank you very much.

I've upgraded my 9.04 to 10.04 last night and the install seem to go well but after the restart, all I see on my screen is blank after the startup logo.  Anyway to correct this?  I'm going to download and try starting the 10.04 by cd and see if this happens again.  If you no of an fix, please email me at sparkcad@gmail.com.
thanks in advance.