black screen at second reboot

I have 11.1 with KDE 4.1.3 installed on my laptop. It had worked perfectly for a couple of months until today when I made some terrible mistake during upgrading to KDE 4.3. Now, for making my computer work I have to start 11.1 from a cd and choose install/update. Then the installer reboots, KDE 4.1 starts and everything looks just like it was before my stupid move. However, next reboots result in a black screen with blinking “underline” prompt. I don’t even get the grub boot screen. So, I have to start from a cd again…

I had tried to find an answer to my problem by reading other posts before I decided to start this thread. If anybody knows of a similar problem already solved, please just redirect me to a right thread.