Burst hydraulic pipe, failed master or slave cylinder, seized pedal pivot. If the pedal won't come back up it's likely to be the hydraulics holding it down - assuming the pedal return spring is still there - so I'd look at the master cylinder first.
For start up I give it about 15 seconds glow in this cold weather and then it's clutch in, right foot to the floor boards and crank. She usually fires up in about 5 seconds with the mandatory cloud of smoke
