Hello guys!
I have pretty weird situation with my n900.

When it is turned off and i plug it to PC or wall charger it starts charging, but after 2 led blinks it suddenly draws "balls" and then turns off.
When it is on nothing happens if i plug usb in.

Is it a battery problem or the charging module?

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

The thing is that my USB port was actually torn from motherboard so i have to solder it back, but it wasn't strong enough
After second soldering problem occurred. I think it can be something from F5300 to L5300, but not charging module itself, because it's quite far away from port.

niqbal, can you say which i.c. was broken in your case?

i will try and visit that shop and ask him exactly the ic that was changed. cheers

Hooray!
I've got it working! The thing was if Data+ and Data- are NOT connected N900 won't charge. No ics were broken
niqbal, thanks for your attention.