D40 battery charged, yet when put into camera there's no reaction?

I've had my d40 nikon a bit over a year now (got it on ebay), and it's worked perfectly. Recently, when plugging in the original nikon battery to the charger, it would blink for 4 seconds (charge) and the cut off. I thought it had something to do with the connection in the actual charger wire, so i bought a new one. When this failed, I tried charging one of my reserve batteries which worked fine. However now that i try putting it into the camera turn it on, nothing works! It's as if the battery's completely dead. What can it be/ what can i do?

Added (1). The first battery was a true nikon one, the second just a generic one. However the charger itself is Nikon, so it has been monitoring the heat… I don't see why they would have reacted that way. The batteries says they're fully charged but doesn't react at all when put into the camera, so i'm wondering whether something could have happened to the camera? Thanks for all the help: D

I'll phone up nikon and ask!

Batteries like all other electronics can often fail - at time with no warning. I'd suggest that you get a new battery, charge it fully and that may do the trick.

Should that not work then I'd get in touch with Nikon because the problem may go deeper.

Call Nikon for a thorough trouble shooting process to see what is wrong with your battery/camera

Generally Nikon Li-ion batteries can last for over 5 years as long as they do not sit fully discharged for more than a few days. This is the single thing that can shorten the life of a Li-ion battery.

Since you bought everything using eBay, I mention generic batteries and charges, since one never knows what is included with a dSLR when buying there

The other thing that can shorten the life of a Li-ion battery is using generic chargers. The Nikon Chargers monitor the temperature of the battery as it is charging and drops to a trickle charge once it starts to heat up. The Nikon charger also stops charging once the battery is fully charged.

It would be strange for TWO batteries to die at the same time. Batteries don't last forever, but I have never seen two fail simultaneously.

I would suggest contacting Nikon at 1-800-NIKON-UX (1-800-645-6679) and request servicing. Have them look at it and give you an estimate for repair (might want to have them do a cleaning/lubrication/timing adjustment while they have it).