very unfortunate. It is a serious issue with n900 hardware by default. Basically, it is not charging. It is one of two, either usb port is slightly damaged/torn from main board OR it is an IC sitting between your battery module and usb port thats damaged. It is an issue which has caused n900 users headaches.

Two months ago, i was stuck at the same juncture. For me, it turned our to be both. I had to get it repaired at a local cellphone repair shop, he resolder the usb port and also had to change the little ic. It cost me abt $35 which was very very reasonable to get it fixed. Once its back to normal, i have made a habit of (not jerking) not yanking the cable off. I use extra care with the usb port.

To make the long story short, you have to find someone who can repair the damaged hardware otherwise skip to a newer cell. Sorry