Default themes are gone! What's happened!?!

[Joshwaa]

Please someone help, all the default themes have dissapeared and my desktop looks UGLY!
I have tried reinstalling light-themes and it hasn't worked :(
Someone help? I'm pretty much a Ubuntu noob.

[Joshwaa]

BUMP. Please someone help :(
The index file and stuff is still in the usr/share/themes/ambiance folder.. what's happened