Looks like you covered the main bases - Drivers, Re-installing, BIOS.
I would be curious if a USB connected device works, since that should be on a complete different system than the PS/2. However, after all the troubleshooting you already did, it could be a hardware-related problem, but to take out the pointing devices AND the PS/2, that sounds like a component on the system board fried, which wouldn't be worth trying to get repaired.
I suppose you've checked Dell's support site for any useful tips. If you want to take a peek at the hardware inside your laptop, they MIGHT have schematics and a prodecure to safely take off the keyboard, etc. I'm not sure what that will accomplish, though.