Here's the info from the link:
I was using wifi on my Pre for a OS update. I left it for like 10 minutes and came back to a dead phone. I hit the power button nothing. Plugging in the phone to the wall or car charger for an extended period of time didn't fix it.
Come to find out if you let your Pre completely die...this may happen. No matter how long you try to charge it, the Pre will not turn on.
FIX: Take off the batter cover, remove the battery. Put the battery back in and hit the power button. The phone should come back on and you want to make sure you start charging this immediately. (This told to me while at Sprint store, I also saw it happen that way.)
I was freaking out that my Pre died in one day. Only the manager who had more extensive Pre training knew about this at the corporate store that I went to to get my Pre fixed. All other associates were not aware of this...until me!
Spread the word so others don't have my same freak out and don't let you Pre battery get to low!