Wont go in reverse

Hi, first of all I would like to say that this is an awesome site. I am new here and I found a ton of information that I could not find anywhere else. One thing I am having trouble with though is my honda accord. I am not sure what year it is because my Boyfriend bought it for me. When he fist bought it, the transmission was bad so he changed it out. ( Its a manual transmission by the way ) Now he says he can't get the darn thing to go in reverse. He say's it makes a grinding noise if he tries to put it in reverse. The weird thing is that if you turn the car off, and then put it in reverse and start it up, it works just fine and it doesn't make that grinding noise when you take it out of reverse. But once you try to put it back in reverse, it grinds again. Only when the car is turned off is when its able to go in reverse. Is this transmission bad as well? Thanks a lot