I have a HP/Compaq s1010z (AMD64) desktop and installed 11.10 from a CD (using the entire disk). So it formatted the entire drive, went through installation and then it ejected the CD and asked me to click the Restart button, which I did. It rebooted fine the first time, but any time thereafter, it fails. Meaning, after the initial BIOS screen, the monitor seems to be stuck in limbo with a text cursor blinking on the top left corner, as if it can't find anything to boot from.
At first I tried reinstalling (reformat entire drive again) - no improvement. Then I did an in-place re-installation (leave home dirs in place, just redo the OS), nothing there either.
Then I put in the 11.04 CD, changed the boot order to CD first, and got the CD menu, chose 'Boot from first hard disk' and it booted fine. The problem is that I can't boot without the 11.04 CD, how ironic!