I have tried installing Ubuntu 12.04 on a desktop pc (with no windows) and the installation went fine.
When I power on the pc, though, after it has recognised the HDDs, it stops and doesn't do anything more. It doesn't report things such as "Missing Operating System" and there is no line mentioning GRUB.
I suppose you need more information, but I need to know what exactly you need to help me - I'm much of a beginner.
Thanks in advance!