I would take bewildered's advice - in one respect - you need access to the source code.
Only a complete IDIOT would expect a programmer to solve the problem without source code. Which does not say much for someone higher up in 'the food chain". Like bewildered, I fear you are being set up to fail. And I have seen this before. Fingers get pointed, and suddenly ITS ALL YOUR FAULT. Try to get another job LATER; with the cloud hanging over your head. WOM (word of mouth) will be your worst enemy jecause you will not have anything that can be used to clear your name.
Get out as quickly as you can; and hope that when the s--- hits the fan, you are long gone!!!! Meanwhile, my best advise is CYAWP - COVER YOUR ASS WITH PAPER. Write memos, document as best as you can, what or WHO is in the way of your trying to resolgve the situation.
Right now, I understand where you are at; as I know s--- about web servers, and putting up web pages; BUT I made that clear to the owner before I started this task. Both of us are proceeding "in the dark". BUT I know that I made that clear before I started out. Lots of luck - you may need it.