My Nikon SB900 is dead! Needed

I've inserted the batteries, but the flash just won't switch on. The batteries are all charged up. The flash is still 4 months old.

Easy then, at 4 months it's still under warranty so contact nikon in your country.

Are the batteries inserted correctly? Are you sure they're charged up? Was it working before ok? Can you hear a whine noise (capacitor charging) or nothing at all?

If it's only 4 months old it'll be under warranty, so take it back to where you got it or contact a Nikon service centre.