["application not found" cannot run malwarebytes]

I have been unable to open any programs like Malwarebytes or itunes. Every time I try, I get the "Open With" box that prompts me to choose a program from the provided list. I am able to access Firfox via Safe Mode by selecting Firefox from the list provided in the Open With box. When I select Firefox a box opens saying I "have chosen to open firefox.exe" and it wants me to "Save File". I choose Cancel instead and am able to access Firefox but cannot run melwarebytes in safemode.

I have read the "I'm infected - What do I do Now?" thread. I cannot run Malwarebytes from my desktop. Each time I try, the "Open With" box opens and says "Choose the program you want to use to open this file followed by a list of Programs to choose from.

I tried downloading DeFogger, but when I try to open DeFogger.exe from the Download list, I get this popup box:

C:\Documents and Settings\Me\MyDocuments\Downloads\Defogger.exe Application not found

I have tried searching on this website and on the internet for a solution, but I don't understand them or they dont seem to suite my problem. I apologize in advance if the "Open With" problem has been covered on this forum. If it is, please direct me to the solution. I just can't seem to find it. Please Help!

Thank you.