Minecraft won't open

I try to open minecraft. everything works pretty much the same at the start, but once I hit [Log In], it says: Failed to launch
fatal error occurred (2): C:\Users-(username)\AppData\Roaming\.minecraft\bin\version (access is denied)

let me tell you how I arrived to this. I opened minecraft. instead of showing the launcher, it just showed the "missing texture" texture. so I thought a file was corrupted. I deleted everything in my minecraft(excepting the saves) and tried again. then, the error appeared, and every time since. I recently installed a new AVG anti-virus software which has messed with the game before, so that could be it.
please fix this.