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The thing to do is to provide power to it steadily for at least 4 hours. If it doesn't charge within that time, then either the battery is defective, or perhaps the charger or charging circuitry. (Rarely, also, the contacts on the battery might be dirty.)
If the Archos tablet is fairly old (1 2/3 years and older) then its battery may possibly have expired / failed / 'broken'. All rechargeable batteries do fail in time.
If the AC Adapter plugs into the Archos to charge the battery, then try plugging the AC Adapter in, then try powering the Archos device On, and see if it runs on the AC Adapter.
If it runs on neither the battery (after abundant recharging time) nor on the AC Adapter either, then it may have a serious problem with the central circuitry (CPU) initializing in the tablet.
How old is the tablet in question?