So, here's what happened:
I've been using Windows 7, but I always wanted to switch to Linux, because you can configure it more than Windows (and easier - so I thought). One day I created a 2 GB bootable USB with Ubuntu 12.04, with persistent mode. I remembered that installing Ubuntu after Windows was not the problem, since grub smartly added Windows 7 to boot menu and everything worked. But that was on my previous PC, and with older Ubuntu.
Now on a Lenovo G565 I booted my USB and started installing. I did manual install in space that I previously freed. Everything went well - till reboot. In grub there was "Windows 7" but didn't work. I tried different device manually (
/dev/sdaX) but none worked.
Then I tried to start Ubuntu. There was an error with graphics (have Radeon 5400), window popped up to choose "Minimal graphic mode" (or something similar). Ubuntu tried to start, but froze on Checking battery state. I tried to boot it several times, with same result. I gave up. Luckily I had my persistent USB (card reader with SD, to be exact), so I could use my laptop.
So, what happened? Ubuntu replaced Windows 7 boot menu with grub. That's OK, but the drivers were flushed in the process. I cannot boot Windows 7 anymore (I can live with that), but i can't boot from CD either. (I tried with USB key in, out, with mouse in, out. Nothing works). I'm stuck with the USB with limited space to install apps.
Now I only want to install any OS to my HDD without formatting it (I think I try minimal-Ubuntu and start from there). But my CD ROM is not working. Question is, how i can accomplish that?