How to force a factory reset or hard reset on Archos devices

Archos 50 Oxygen+ Archos 50 Oxygen+
Archos 94 Magnus Archos 94 Magnus
Archos 101 Magnus Archos 101 Magnus
Archos 101 Magnus Plus Archos 101 Magnus Plus
Archos 101d Neon Archos 101d Neon
Archos 96 Xenon Archos 96 Xenon
Archos 101b Copper Archos 101b Copper
Archos 50c Neon Archos 50c Neon
Archos 40d Titanium Archos 40d Titanium
Archos 50 Helium+ Archos 50 Helium+
Archos 55 Helium+ Archos 55 Helium+
Archos 101 Xenon Lite Archos 101 Xenon Lite
Archos 70b Copper Archos 70b Copper
Archos 70 Platinum Archos 70 Platinum
Archos 101c Platinum Archos 101c Platinum
Archos 50e Helium Archos 50e Helium
Archos 70c Xenon Archos 70c Xenon
Archos 80c Xenon Archos 80c Xenon
Archos 50c Platinum Archos 50c Platinum
Archos 55 Platinum Archos 55 Platinum