if u are using nvidia graphic card most probably this problem arises i too faced this problm
u have to edit the xorg.conf file which contains the info about your screen resolution and install graphic card later to have the ubuntu working for me i cant even boot the 10.04 cd (i mean cant see after booting) google it . . i just dont want to woory a lot so i didnt did the solution -- l...@iitd - http://tinyurl.com/ycueutm
