To Factory Reset or Hard Reset your Archos:
- From a Power-Off state, hold down the Volume Down (or Volume - ) button, and while holding it...
- ....Press and release the Power button while continuing to hold down the Volume Down button... until the tablet restarts and shows the Android logo and a bit past that, then release the Volume Down button.
- you should, after a minute or so, see the choices:
Fastboot Recovery Clear Storage SIMLock
and use Volume Down button to select Clear Storage
Then press the Power button to activate that choice... when prompted as to whether to delete data, or if you see a YES and NO choice, choose YES.
If that fails to help but you did see the Clear Storage option, try it again, only select Recovery this time, and see if there's a Wipe Data And Factory Reset option there, and choose it instead.