Subwoofer Trouble shooting advice

Somewhat of an audio beginner here, so bear with me. Recently ran into an issue with subwoofer in my system.  I'm running mono blocks to each speaker and have 2 subs set up with L & R inputs to each sub from pre-amp and crossover set to variable on my sub.  I recently unplugged one of the subs because it wasn't preforming well and the other just stopped working.  Didn't change anything else in the set up and now the one good sub only plays if crossover is set to Bypass(LFE in) which is way to boomy.  

I feel like I've tried everything, plugging other sub back in, checking cables, resetting everything and it will not play on previous settings.  Any advice?