I'm having a very similar problem to the one described above. Earlier this evening I unboxed a completely new Dell Venue Pro. It was carrier locked to T-Mobile, but I have subsequently unlocked it with the code provided to me from Dell directly. My plan is to use the phone on the Rogers network in Canada, and right now there is no SIM card in it.
Anyway, the phone refuses to charge properly. When it has the battery in it, and I try plugging it into the wall, the phone shows a full screen icon of a battery with a AC plug on it (I assume this means the phone is fully charged.) However the moment I unplug it the screen goes dark and there is no way of turning it back on. I've tried holding the power button, I've tried pulling the battery, putting it back in, and then holding the power button. Nothing seems to work.
If I plug in the phone into the wall with no battery in it. I can get into the OS. If I then put the battery back into the phone while it is still charging, it'll show that the battery has no charge. After a few minutes (in the ball park of 5-10) it'll again show the full screen icon of a battery with a AC plug on it.
I've compared this to my friend's Samsung Focus which was plugged in when it has no charge. The Samsung focus will show a full screen critically low battery icon when first plugged in, then as it charges we'll get a full screen low battery icon, and then the Windows Phone 7 OS itself will load. (It is still not fully charged, so I do not know if we ultimately get the full screen icon of the battery with plug.)
Both phones (Samsung Focus and Dell Venue Pro) have been charging for over 2 hours now. The Samsung Focus is in the WP7 OS and shows an increasingly charged battery. The Dell Venue Pro still has that full screen battery+plug icon.
The only way I can access the WP7 OS on the Dell Venue Pro is to take out the battery and plug it directly into a wall, or directly into the computer. I have succeeding at carrier unlocking it and upgrading the OS all the way to Mango using this approach. However the phone just refuses to run on battery power.
Has anyone else run into this problem? Do you think it is the phone, or the battery itself? Any advice would be appreciated.
P.S. Sorry to bump such an old thread, but I'm a n00b, and the video said to find a thread related to my problem, and post there.
Edit: So the Samsung Focus finished charging. It lets me interact with the WP7 OS, and does not have the full screen battery with AC plug icon. Although it does have a much smaller version of the icon on the top of the screen where the remaining battery icon is.