2001 Pontiac Sunfire Car loses power, will not start

Electrical problem
2001 Pontiac Sunfire 4 cyl Front Wheel Drive Automatic 72k miles

For the last few weeks, the car has been losing power while I'm driving. All the dash lights will darken, then turn back on immediately. Most recently, the car occasionally will not start. Depending on how the fuse panel is shifted, the engine will turn over but never catch, OR will catch but immediately die. "Aggressively" seating the fuses worked last week - the car started immediately. Now nothing I do seems to work.

When the ignition is on, I can hear the hum of the electrical system, etc but the dash lights, radio etc do not work.

Thanks!