"Open with" problem, can't open regedit or cmd?

Hi, I recently removed a virus by the name XP Total Security 2011 using ad-adware and avast. After its removal (i think its gone) every time I try to open something, I'm asked to choose a program to open the application with. I have looked online for its solution, but they all seem to require opening RegEdit and Cmd. The problem is the same "open with" happens when I try to open any of these. Please help! I am literally stuck using only the browser. thanks so much!