Ubuntu 13.04 doesn't boot up after I upgrade from 12.10. I have tried to edit the grub (nomodeset), but it still doesn't work.
I have a HP Pavilion dv6-2153eo PC and a ATI Radeon graphics card.
I can't help with a boot because I do believe that there are a few problems with the upgrade! There is a note to this affect in the docs. Also the graphics change again back to the stock solution. So if you don't get an answer, you will have to do what I myself did in this situation. Admittedly I do have another Ubuntu 12.04 partition, but a Win7 partition might also work.
Get into the other partition and save all your /home/myname files somewhere safe on the other partition. Ensure that they have the correct ownership, i.e. "myname", or group me "myname". Now download the ISO for 13.04 and burn it to CD or DVD because the USB support is no longer [another note for that].
Install 13.04 all new onto the correct partition, with or without swap. Copy over any hidden home files etc as necessary. Good Luck!