Hey,
Did you check if the bootable flag is on /dev/sda1 (which I assume is the
first partition on your primary drive)? Newer motherboards (like min - a
g965), refuse to boot, if they do not see a bootable flag on the first
partition.
The easiest way to change this is with 'gparted' that comes with ubuntu
gutsy (the flag can be turned by using an option in a right-click menu).
In case that fails, you can always try the command line parted to switch on
the bootable flag.
--
Pranesh Srinivasan
