Ubuntu 11.04 (Natty Narwhal) freezes after booting (before logon screen)

I've upgraded Ubuntu 10.10 to Ubuntu 11.04 on my HP laptop, and the new Ubuntu started freezing after booting. It didn't boot in the recovery mode either. I tried to install Ubuntu 11.10, but it didn't boot as well.

Tried to use the nomodeset option (added it by pressing the E button in the grub), but it didn't help either. I don't really know what causes the problem. Hitting the ESC button or CTRL+ALT+F1 before freezing didn't help to show anything on the screen.

Then I decided to install Kubuntu 11.04. It booted without any problem. I didn't like Kubuntu, so I installed unity-2d and lubuntu-desktop from it by running

Code:

sudo apt-get install unity-2d lubuntu-desktop

in the terminal. I chose the GDM windows manager because I got used to it.

Now I can choose between unity-2d, lubuntu (LXDE) and kubuntu when logging in.

I guess the problem is caused by unity. But instead of installing Kubuntu I would recommend to install Lubuntu (doesn't have official endorsement from Canonical) or Xubuntu. Both of them use lightweight windows managers.