1997 Audi Quattro Manual

I have a '97 Audi A4 Quattro 1.8 that won't start. When you turn the key absolutely NOTHING happens.
Here's what lead to the issue: I started the car and heard a "click" noise that was unusual. While driving everything electrical stopped working - the directionals, lights, air blower (which showed on the console that it turned on, but no air came out, and then it shut itself off). When I arrived at my destination, the key wouldn't come out of the ignition. I was able to start the car back up, with no problem, and then drove home. I forced the key out of the ignition and all the electrical came back on, but now the car won't start up. The ignition switch has been replaced and we've tried bypassing the lock cylinder but it still won't start. I replaced the ECU yesterday and again, nothing. We've checked the security system and there were no issues there either. Any suggestions would be greatly appreciated!