Ubuntu 10.04 shipped with some bad ISO that were released on the release
date, but corrected a few days later. This ISO botched grub2 among other
things. Make sure that you have a updated ISO first.

When I have installation problems the first thing that I do is boot into
text mode. To do that press F6 at the grub screen and remove --quiet splash.
Now you can see text scroll by and see where the loading fails. Next you can
try so boot parameters to work around the problem. Common problems are
graphics problems and kernel panics, usually caused by a conflict due to a
memory or IRQ conflict, or a weird BIOS setting etc.

Ubuntu 10.04 made many changes that could lead to problems. Graphics cards
were a problem for many. Old drivers did not work and the open source ones
they used to replace them did not do the trick with Plymouth (also new with
this release). Also HAL is gone and Devicekit is in, so that may be a
problem area.