A hard reset will erase all your data, contacts, applications, and settings, returning the phone to the exact state it was when you unboxed it. Back up your files via USB Mass Storage mode before proceeding if the device still turns on.
If your device is stuck in a boot loop, "frozen," or you have forgotten your lock code, a standard menu reset won't work. You must perform a full reflash using a computer. This is the only way to return the to its "out-of-box" state. A computer (Windows, Linux, or Mac). The Maemo Flasher-3.5 tool. The original N900 Firmware image (.bin file). Steps to Flash: How To Restore A Nokia N900 Smartphone To Factory Settings How to Hard Reset NOKIA N900
You need two specific files:
Note: Do not use the -R flag for eMMC flashing. A hard reset will erase all your data,