try changing the title of your thread so more people can answer your question.
maybe it is a grub related problem . try booting off the live cd of ubuntu whatever version you have and type:
sudo apt-get install grub
then follow THIS
also it might be something related to xorg , in wich i'm not an expert by no means and maybe another linuxer around here could help on this one [ maybe getting an older version ov i dont know what xorg or some driver ]
ARE YOU USING NVIDIA graphic card ? does grub actually show up ? i mean .. try and press shift and select an older version of kernel from there or the repairmode or whatever it is
try giving us more details about the problem