All I got was the usplash screen and when I Alt-Ctrl F1 'd i saw "mountall: disconnected from plymouth". No matter what I tried couldnt get any further.
It happened to me once before and in the end I reinstalled which wiped everything. Now I'm a little more seasoned I knew this wasn't going to be necessary.
So I used my 10.04 LTS liveCD and started searching for solutions. I managed to find the following info which poved most useful because it allowed me to mount my HDD FS within the liveCD GUI and work from cmd line as though I were in the HDD OS: http://ubuntuforums.org/showthread.php?t=422523
Also quite useful:
http://galigio.org/2009/11/29/how-to-repair-a-bad-upgrade-on-ubuntu/
http://serverfault.com/questions/8540/recover-from-shutdown-during-ubuntu-distribution-upgrade
http://ubuntuforums.org/showthread.php?t=186672
http://www.ubuntugeek.com/easy-way-of-mountunmount-iso-images-in-ubuntu.html (used this to download and mount the alternate upgrade cd, which is how I eventually fixed my upgrade)
http://serverfault.com/
http://ubuntuforums.org/
http://www.ubuntugeek.com/
Essentially what had happened was that after usplash the nvidia drivers werent loading, so I removed the xorg.conf file, and replaced it with the xorg.conf.failsafe. This step got me booting into a low res gnome desktop, yaaay!
I then Alt-Ctrl F1 'd to the shell, and mounted the ubuntu-alternate iso I had downloaded when I was in the liveCD, and which I ha copied to my home folder on my HDD from there.
Once the iso was mounted I simply ran:
sudo /media/cdrom/cdromupgrade
and ten minutes later everything was fixed and my desktop was up and running 10.10 !
Good Luck! :)
