Changing themes on windows 7 on its own?

I have recently upgraded to windows 7 and it was fine until the other day when it automatically changed to windows classic theme and now I can't get it back on to windows 7 ultimate theme because all the themes are blanked out? how do I get it back? :S



Thanks Samuel :DChanging themes on windows 7 on its own?
You are probably in Windows 7 XP Mode : read this http://www.theregister.co.uk/2009/05/01/windows_7_xp_mode_review/Changing themes on windows 7 on its own?
Try this:

Control Panel---%26gt; Scroll down till u find ';Performance information and Tolls';-----%26gt;Click on it and on the right hand corner-----%26gt; Adjust visual effects.

Then there are two options:



Click on : ';let windows choose what's best for my computer'; then click apply and see what happens

OR

';adjust for best appearance'; and clock apply and see what happens.