The way I read the OP's last couple posts, after removing the lens and film back, he found that the bellows was misfolded badly enough to protrude inside the body at infinity focus setting and block free movement of the mirror. If that's the case, it's got nothing to do with metering or operator errors, it's just a badly abused bellows. I'd already advised him, in PM, to look at a new bellows or a replacement body (to designate the one with bad bellows for parts) -- didn't realize either bellows or bodies were that inexpensive (by about a factor of two).