5d2 hotshoe issues

My 5d2 is giving me issues regarding my flash, and I have come to the conclusion it has something to do with my hotshoe.

Tonight when taking a few photos, I noticed my AF assist beam on my quantum flash wasnt working. When I got home I tested the flash with the 7d and it worked just fine. Same with a few other flashes on my 7d.

Put those flashes on my 5d2, and now not only with the AF assist beam not work, but the flash wont fire. The camera and flash talk to each other - I can change the exposure on the camera and watch it change on the flash, but it doesnt fire.

What can cause this, or the better question, what can fix this? Will it be a pricey fix, or should it be fairly simple/cheap? I am planning to talk to a camera repair shop tomorrow.

I don't have experience with this. I would put another flash in the hotshoe to test it.
If both are no good with 5D2 and both are good with 7D, it's probably need to be sent to repair center.

Maybe some screws loose.

Not sure about the Quantum flash, but with a Canon 430EXII it may be that the auto assist isn't firing. In several threads several people state you must enable AF assist BOTH in the camera's C.Fn III-11 and in the Speedlight's custom function, or it will not fire. Also, the AF assist will not fire if the camera considers light sufficient. That may mean that the camera will focus on the contrasty edge between a dark tie and a white shirt, when you actually want it to lock on to a face. The camera may need AF assist for the face, but not for the tie, and select the tie, in spite of that not being your intention.