I'm trying to flash my N800 to the factory defaults, but it refuses to connect to my computer. I'm running the Update Wizard provided by Nokia, and it simply won't find the device.

No, I can't give you a better error message. There isn't one.

Yes, the battery is charged.

Yes, the USB cable is working. My computer finds the SD cards in it when it's on and connected.

Remember that when you switch it on using the power (on/off) button while holding the "going back" button (the one on top of the home-button, try the "going back" instead of "home" button here!) only release it when you see the USB icon appears on the right corner!

Charger needs to be unplugged, the device needs to be off, and the USB cable needs to be plugged in to both the N810 and the computer (preferably directly to the computer—no hubs).

Uh, no the escape button wont do a damn thing. You need the Home key on the N800 (the bottommost key on the face), or the Swap key on the N810 (the topmost key on the face).

Hold down the Home/Swap key, and turn the device on. Release, as nhanquy said, when the USB icon comes up.

Assume I'm doing everything right, but the computer just isn't playing along. Because all the recommendtions so far were alrready covered.

Sorry if I sound snarky.