He mean, that everything seems like no data lines, despite fact, that when he probed them (from behind port) to testpads under battery, they've worked perfectly.

Can-opening a usb male plug or female port, connecting to teared-open microUSB cable (thus creating easy tet solution for socket itself) seems like good idea. If it isn't internal damage of usb port, then I have no clue wtf is going on with Your device.

/Estel

/Edit

Or even without tearing down usb plug - just cut open a microusb cable, then plug it into N900, and probe loose cables with testpads under battery.