Of course, there's a good reason why it's so difficult to find out the key....it stops someone else using your connection. Moreover, if someone "professional" has set up your router, they should have changed the admin password to prevent unwanted access.
Are you sure you don't have the router admin password or the WEP key? My Mum didn't know hers but after a bit of rummaging in the box, the key was written on a piece of paper. If you really can't find your key, I think your best bet is to do as someone else said and that is factory reset your router. The manufacturer provides this capability just in case you forget the password.
If you do go for a factory reset, it will also remove the configuration of your network too. So, it looks like you might have to invite JD round for dinner with an exclusive cheese board and carefully selected wines and get him to sort it while you relax and listen to some tunes.