The F3 (TTBOMK) has an electronic release. Try removing the batteries and waiting a few minutes.
Try raising the mirror my hand. Then play with releases and wind levers. Try fiddling the sprockets while depressing the rewind button. See that the motor wind interconnections are free - try moving the drive wheel back and forth using a pair of needle-nose as a spanner wrench.
SLRs have all sort of synchronization levers and stuff - sometimes one of them gets out of synchronization and the whole thing gets jammed up. Someone may know the magic sequence to get it unstuck but often just playing with everything can work.
My mother takes this approach with her TV, DVR and set top box. She calls up and complains "I don't know why it doesn't work, I've pressed every button on all the remotes at least three times and it still won't work...", by this time the menu system is in Romanian and the TV is tuned to community access cable in Tristan da Cunha.