Uxtheme.dll Error

my brother was messing with my computer trying to install a theme. by doing so he replaced the uxtheme.dll file with another file. when the computer was rebooted an error popped up stating that the uxtheme.dll file was invalid. after pressing 'ok' nothing loaded except the wallpaper. i have tried going into safe mode but it is the same deal. i am able to access the CMD and the window that appears when you 'CTRL+ALT+DELETE'. i am trying to avoid wiping out everything on my computer and start anew but if that is the only solution please say so. i hope you can help with my problem, it would be greatly appreciated!

 

Start >> Run >>> sfc /scannow [xp cd needed]

 

IF the file checker doesn't help
then Boot into the recovery console

expand d:\i386Uxtheme.dl_ c:\windows\system32\Uxtheme.dll