I guess that means you have to flash it. Were you playing with config files?

Follow these instructions:

http://www.mobile-geeks.com/how-to-u...ing-n900/2037/

You need one of the "maemo_flasher-3.5_2.5.2.2" files, depending on your desktop operating system (heard there might be problem with Windows 7 or something). Then you need one of the "RX-51_2009SE_2.2009.51-1" files, depending on your region. Then follow the instructions. Should take about 15 minutes (after downloading).