I had a same problem. I revived it by using this method as described by team23w,
Originally Posted by nathanail
"If you can't pull a charge from the TP wall plug charger, and you know the cheap TP USB cable hasn't gone bad, here is the next thing to try: Go get a standard, low power, USB charger (like for your cellphone, or if need be use your computer's regular USB port). Plug the bugger in on your wimpy little USB cell phone charger and let it trickle charge at that low, 1000mAmp rate for a couple of hours and see what happens. I revived mine doing this, after the TP wall charger did nothing for 14 hours. It appears that if the voltage drops too low, the only way to charge it is using the standard USB voltage and not the higher voltage normally fed out by the TP wall plug or Touchstone. Definitely try this before you go through all the trouble of pulling the thing apart. "
In my case I used non-HP usb charger to charge the touchpad for 6 housrs or so Disconnected. Pressed various buttons. One that lighted the menu button light was: Pressed and hold down menu button while rapidly pushing the power button. Menu button started to flash, then the power plug symbol appeared. I placed the Touchpad onto touchstone. After 5 minutes, low battery symbol appeared on screen. After couple of hours of charging it rebooted. I made sure it rebooted to WebOS and not CM9. It's been working fine ever since. Only change I made is to make sure battery doesn't fall below 30% level while on CM9 or I charge via Webos.
Hope this helps.