Having a good background in electronics, I can only suggest this:
1- Make sure that the battery is in good condition and that it is fully charged. Some rechargeable batteries that have not been used for a long time might give wrong voltage readings because of their faulty condition. They just do not deliver the necessary electric current/power. Get a new battery.
2- Make sure that the battery contacts are clean - also inside the battery compartment of the camera. Storing batteries inside an electronic unit for a very long time might result in corrosion of the contact terminals that will create high electric resistance, not being able to power up the unit - not to mention a degraded state of the battery. Clean the contacts. A new battery might be needed.
3- Has the unit been exposed to any falls or mechanical vibrations? This could have damaged or displaced any mechanical contacts/parts inside it. Get someone qualified (service technician) to check it. It could be fixed, but it could also not be worth fixing it.
4- Should points 1, 2 and 3 be ok, we are then talking about a *really* faulty unit. Has it been exposed to very humid air during storage? Salty atmosphere (by the beach)? This could corrode the terminals and electronics inside it. Sorry, but the only way to fix it is by getting a new unit and battery.
Hope that this helps.