1. turn off your phone, and it needs to be at least 3/4 charged, i would recommend fully

2. install Maemo-flasher on your pc. download here : http://tablets-dev.nokia.com/maemo-d...-downloads.php (choose the one you need for your computer)

3. download the right firmware for your device (for me it was "global" and the latest is of course pr1.1 - 51) here : http://tablets-dev.nokia.com/nokia_N900.php

4. copy the .bin file of your downloaded firmware to C:\Program Files\maemo\flasher-3.5\

5. launch cmd (can be done with execute)

6. type in : cd c:\Program Files\maemo\flasher-3.5 and press enter

7. then type : flasher-3.5.exe -F "name of the downloaded firmware" -f -R and press enter
(looked like that for me "flasher-3.5.exe -F RX-51_2009SE_1.2009.51-11_PR_COMBINED_MR0_ARM.bin -f -R" )

8. you should see now a new window where "Suitable USB device not found, waiting" is written

9. push "u" key on your n900 et plug it in via USB cable to your PC and keep "u" hold till the phone is recognized, its screen should be white with nokia blue logo