Try use the terminal as it shows better what have gone wrong.

I am not sure if this is the correct path for the log.. but if you use "leafpad /home/user/.hildon-application-manager/last-update" it should show you a log. You will need leafpad installed.

You did right by this..
sudo gainroot
apt-get update
apt-get install libsdl-ttf2.0

But try with moodlight instead..
sudo gainroot
apt-get update
apt-get install moodlight

Or all not upgraded..
sudo gainroot
apt-get update
apt-get upgrade

and..
apt-get autoremove

If you want to install many programs at the same time.. then just add with a space between. "apt-get install moodlight leafpad libfribidio" e.t.c.