Car Cranking not starting, electronics don't turn off
 

So I've just had my 350gt serviced and it was working for a few days, but when running late for work it failed to start, cranking but nothing else. This used to happen intermittently but seemed to have been fixed. That wasn't the weird part though, as when trying to turn the car off, the electronics wouldn't turn off, the dash lights and screen staying there. There was also an LSD dash light in the middle of the cluster I haven't seen before. Then, the electronics just shut down. The windows didn't pop back up when the door closed, the car wouldn't even crank and all the interior lights were off. But for some reason the headlights and taillights just wouldn't turn off, no matter what. For now I just disconnected the battery and sealed the windows, as more rain is coming. There was heavy rainfall all of last night, so might that be the cause? Car is an unmodified 05 350gt with 50000 miles. Any help appreciated :)

If your lower windshield cowl is somehow not tightly affixed to the glass on the passenger side (or drains clogged and you have overflow), or you don't have the underbody shield on, water could have gotten into the IPDM below the battery. If those drains are plugged with debris (not uncommon), then the reservoir fills with water and the IPDM goes haywire. If it is wet, remove it and dry it out slowly... don't try to accelerate with heat.... Put it in front of a fan, or you can try the "put it in a bag of rice" trick.

Definitely sounds like water getting into the IPDM.