Factory Reset Gigaset DX800A:

A factory reset Gigaset DX800A is a software restore method of an device to its original system state. This will erase all of the information stored on the device in an attempt to restore the device’s software to its original manufacturer settings. Doing so erases all of the data, settings, and applications that were previously on the device. This should be done as a last resort usually to fix a software issue. This can also be done to restore the device to its original settings. If your Gigaset DX800A is dead and does not respond to this, you should test the power supply as it could be faulty.

Reset proceedure to factory default of Gigaset DX800A: