First, boot into recovery (the 'Volume + Power + Home Button' thing) & try a factory reset. If the problem persists, the only way you're fixing it is by flashing a stock rom with Odin.

As you can't seem to get your PC & phone to recognise each other, you need to find Hopper8's 'Odin troubleshooting' thread stickied in General, and do as many of the troubleshooting steps in that thread as many times as you need to until you get a successful flash of stock.

This is the only way you'll be fixing your phone for your 'something in two days'.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?