1. Open the Command Prompt (Start then Run or hit the Windows Logo key + R) and type cmd in the box then press Enter.
(Once the C:\Windoes\system32\cmd.exe DOS box opens on your Windows desktop right click on the title bar and make sure that the “Insert Mode” box is checked in properties > options
2. Change the directory to the Flasher's path by copying and pasting the following command after the DOS prompt (you may have to hit the enter key after doing so):
(Your DOS prompt should have now changed to something like this: c:\Program Files\maemo\flasher-3.5> )
3. Unplug the charger from your freshly charged and backed up N900
4. Hold the u key on the device keyboard and connect the USB cable from your Windows machine at the same time. Once the USB icon can be seen in upper right hand corner of the dimmed screen on your N900, release the “u” key.
5. Flash your N900 by copying and pasting the following command after the c:\Program Files\maemo\flasher-3.5> DOS prompt (you may have to hit the enter key after doing so):
flasher-3.5.exe -F RX-51_2009SE_10.2010.19-1_PR_COMBINED_MR0_ARM.bin -f -R
(Note: Change [RX-51_2009SE_10.2010.19-1_PR_COMBINED_MR0_ARM.bin] to appropriate file name if another image is used. )