^^ I really don't have the time to do a proper write-up, but I feel your pain and don't want to leave anybody twisting in the wind.
Brief background: The TouchPad's charging is controlled electronically. It checks to see if the battery needs a charge, if the battery's temperature is in a safe range and other factors before it will accept a charge. The TouchPad needs power to make all of these measurements and decisions, so if the battery level falls too low, it won't even recognize the charger. There is another thread here that discusses a procedure to physically access or even remove the battery and charge it with an external battery charger -- pretty dangerous stuff, unless you know what you're doing.
What seemed to happen with mine was that I was able to put the TP into a low-level loader mode which allowed the PC's USB connection to charge the battery enough to allow the TP to recognize the wall charger.
Step 1: Even though your TP may be off, and may appear to be dead, you have to make sure that it really is off. Press and hold the Power Button and tap the Home-Center Button (the one at the bottom of the screen) 20 times. Really, the first 15 presses should perform some kind of emergency power-off, but do the 20 presses, just to make sure. You won't be able to see any difference, but now even the TP will know for sure that it's turned off.
Step 2: Plug the TP's USB cable into the micro USB connector on the bottom of the TP, and connect the other end of the cable into a USB port on the back of your desktop PC. The reason I say plug it into the back of the PC is that some PCs don't provide the same voltage to extra USB ports on their front panel. The same could be true of a laptop.
Step 3: Make sure that your computer's speakers are turned up enough for you to hear whatever chime your system sounds whenever you connect a USB device.
Step 4: I'm not sure about this key combination, but it's one of the two and you'll know you've succeeded when you hear your PC chime: Press and hold both the Power Button and the Volume Up Button for 60 seconds (or until you hear the chime). If you haven't heard the chime after 60 seconds, repeat Step 1 and then try holding a three-button combination of the Power/Volume Up/Home-Center buttons for 60 seconds (or until you hear the chime). Your PC may discover a new device and try to install drivers; if so, do what you can to install them, and don't panic if you can't.
Step 5: If you heard the PC chime at any point in Step 4, you might be able to confirm that your PC has knowledge of a Palm Device on a USB Port by going into Device Manager on your PC (right click on My Computer and select Properties, then Device Manager). You should see the Palm device listed under LPT or Serial Ports, or maybe under USB. If you don't, proceed to Step 5a:
Step 5a: If you have not been successful in hearing the PC's USB-connected chime and you can't find a Palm device listed anywhere in Device Manager, repeat Step 1 to make sure the TP is turned off. Then repeat Step 4, but use the Volume Down Button in the place of the Volume Up Button. The combo of Power/Volume Up or Power/Volume Up/Center-Home buttons should get the TP recognized as a Palm Device, while the combo of Power/Volume Up or Power/Volume Up/Center-Home buttons should get the TP recognized as qhsusb_dload. I'm pretty sure this mode is for a low-level boot-loader (that you hopefully won't need). The qhsusb_dload mode will try to install drivers (which can be found on the Web).
Step 6: No matter what level of success you achieved in Steps 4 and 5, allow the TP to sit and hopefully charge a bit from your PC for a while. If you check back after 30+ minutes and the TP's back feels slightly warm, you're in a good place.
Step 7: Plug your TP into the wall charger and leave it. If it hasn't come back to life within an hour, check to see if it is warm. If it's stone cold, I'm sorry. You might have better success at the above procedure a second time through.