Posting on behalf of my OH.

She's got a BC Rich Warlock.

Having problems with the jack port, it must be loose or something because the lead only works when its held in a certain position.

Know its not the lead as tried more than one and they work on my Bass fine.

I'm hoping its just a case of tightening some screw or something?

Any help would be appreciated.
Unscrew the jack, pull it out of the body, check if both wires are soldered good - move them with your fingers, if the part where the solder is moves you need to solder them again.
Check the jack inside -is it rusted? Check the tongue part sticking out too. Connection with the cable may be bad. Clean the rust off.
Ultimately buy a new jack and solder it.
I'm having the same problem with a strat. It's probably just a loose wire or something.
It sounds like the jack from your cable is coming into contact with one of the wires of your output jack.

If the jack from your cable comes into contact with either one of the wires soldered into the lugs of the output jack (ground or hot) it will short out and you won't get any output.

Re-solder the hot and ground to the jack, but make sure it won't come in contact with your cable's jack. Try and make sure the exposed (unsheilded) portion of the wires aren't on the inside and prone to shortages. Best bet is to wrap them around the hole in each lug :-)