Seats, Locks, Side Windows, Horn won't work
 

I have an 07 G35 Sedan and the seats don't move back and forth ( passenger side doesn't move at all ).. seat memory doesn't even light up. Side Windows won't move, All 4 doors have to be manually (un)locked. Annnd horn is faint. Pretty much non existent. I've changed the anti theft fuse to see if that would help but nothing. Any ideas/help

Sounds like you lost a ground so.ewhere, check the battery cables on both ends. BCM ground is right behind the panel for the instrument cluster, you can Google the location.

Also check the fusible link and everything in the ipdm, might have simply blown out something.