ubuntu can't boot

[zaqwes]

I've had ubuntu 11.10 with 3.0.0.14 kernel working but sound was off, so I was using 3.0.0.13 which started having some problems. So, I decided to upgrade kernel to 3.1. Upgrade went perfectly (no error messages) but after reboot there is violet screen.

I turn computer on and I have GRUB properly working, I choose 3.1 version and I have the violet screen or there is logo with dots, they turn all red, logo dissapears and I get violet screen. ctrl+alt+f[sth] doesn't work, the same with power button. I tried choosing older kernel version, I get black screen with some things turning on, everything is ok, and it stops (no log in screen) I can press power button and it works, and turns computer off.
I made livecd on pendrive but it gives "boot error". I wnet to recovery mode and tried startx(gives blackk screen with locked mouse), initx (white terminal window in the corner in which I can't write anything). I don't now what I wrote but it gave something about Xorg problems. I also got i915 symbol problem ( which I think I've seen before with working system I have intel i5 and I've read it always gives it when there is no other graphics card on). I found a lot of similar problems but most of them was either to update, or nVidia problems - I have radeon card hd 5650

I tried

apt-get install --reinstall linux-image-generic

it went without problems but showed me that I have 3.0.0.15 kernel version