Wont start as there is no power to the deck

Well it could be several things a safety switch for the seat, mower deck etc not in the proper position. Blown fuse,bad ignition switch, burned out solenoid. if you jump the battery side of the solenoid to the small terminal and nothing happens, it's the solenoid. If it turns over check the other items. Start with the fuse that powers the ignition switch.

check for safety micro switches on the cutter deck, lift, height adjust or belt drive

Disconnect all power and check the large fuses to see if they are not blown.

Check for power to the clutch from the switch or could be a bad relay

You cut the speaker wires and your car won't start??? Sounds like you cut more than the speaker wires.

Yes the is a fuse on the back of the deck, You have to take the deck out,

could be a few things-pull the unit out and make sure the power and memory and ground wires are all solidly connected.check your fuses may be a little tiny one inserted into the back of the deck itself-check fuse box also. if you still cant get it to turn on get a volt tester or test light and make sure that you are getting power to the deck.

check the fuses on the stereo and on the car

1. Check for internal fuse.
2. Check the power transformer.
3. Check the rest of the power supply.

there are sometimes fuses on the power wires going into the deck, have you tried removing the deck to check if there are any that may be blown?