I was in the same boat as Thunderer tonight...
I installed a theme (wasn't asked to download anything), and stupidly hit the Yes to Continue Anyway button before waiting to see the new bar etc load.
My desktop was blank (just the old theme wallpaper), with no menu's etc and no right click.
After hitting a few buttons (randomly..) I found that I could Alt-Tab to open my browser which I had been running beforehand, so I came here looking to see if someone else had had the same problem.
I couldn't get to Task Manager at all, ctrl-alt-f1 and ctrl-shift-esc both did nothing.
I ended up doing the same as Thunderer and installing the Omar installer again from online.
It's all done, but I have to restart for it to take effect.. I expect it will be all good once I do.

Really guys.. I appreciate all the ppl that attempt to help the 'noobs', but the few of you who just leave nasty comments because you're sick of the less 'geek-genius' types should maybe just ignore they're comments rather than put them down?
It doesn't get anyone anywhere; just shows arrogance.