Update 2012/09/20: Since I wrote this, I realized that my tips below only work randomly and not reliable enough to be labelled as solution. Maybe it was random luck that made it work. Sorry for that. I was about to delete this post, but there have been few suggestions by the reader in the comments that may help instead.
My Nokia E7 simply didn’t want to charge via USB. From Google I know that if the phone is completely dead it may take a while (some say up to 15 minutes) to recognize the charging, but in this case, my phone was not dead. I still have at least one bar of battery, I simply want to charge it, I plugged in the USB cable in the usual port in my computer, and nothing happened.
If that’s the case with your E7, then maybe these tricks below help.
Turn off the phone. Turn off the phone while keeping the USB cable connected. After few seconds, your phone may beep and start charging. The light on the phone’s USB port should blink five times, and the phone would start up (i.e. showing the white splash screen. It’s not the full blown start up but rather start up to “dead” mode just to display that charging is in progress), and you’ll see the light on the phone’s USB port is lit continuously.
If charging doesn’t start this way, disconnect the USB cable, wait for few seconds, and reconnect it. It often fixed the problem for me.
Once charging has commenced in “dead” mode, you may try to start the phone. I found that in most cases the phone would continue charging in “running” mode if you start it this way.
Change to another USB port. Recently, the above trick no longer works for me. If I plug the USB cable in the same USB port in my computer that normally works (while the phone is dead), the light blinks five times, then the phone boots (showing the white screen), but then it stops, and the phone’s USB light indicator is off. The battery indication is shown, but it’s not moving (i.e. it doesn’t show that charging is happening).
When this happened, I found that moving the cable to different USB port in my computer works.
Hope these help.