My guess is that it didn't finish by writing the grub to the boot section I
think I
would use the windows there and download the 10.04 after the final release
on
the 29th of May, burn a live CD image and load fresh from that CD. One other
suggestion would be to download Gparted image and burn that to a CD and keep
it around. With that CD you can see your partitions and even see what any
labels
are, you can even resize any partitions you have currently before doing the
load.
It is nice to have tools like that available for personal use during
testing.