This is what I've got. I cannot boot and I see the two of three little lights on the keyboard blinking all the time and the cooling is working on full power, almost.
I saw in other askubuntu topic suggestion for memory test. I did it. I didn't have any errors.
I am 99,9% sure it is not a hardware problem, because I have Windows 7 and I can boot it and it works just fine.
This problem came without any warning or something. I just turned off the laptop one day and at the other day I couldn't boot.
From recovery mode I get this:
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and then remove 'quiet' and 'splash' from the kernel line if present. You can then press Ctrl-X to boot. This might display a little more information that could be useful. Edit: tumbleweed's suggestion is better, try rescue mode – benwh Jan 05 '12 at 07:56/var/log/kern.log
from your Ubuntu partition using a Live CD? – Lekensteyn Jan 05 '12 at 10:05