my 4300 is dead what's wrong and can it be fixed

batter charged, but camera doesn't power up. camera battery replaced and camera still doesn't power up.

Well, could be that although you're battieres are charged, the contacts are dirty. Try cleaning them with a pencil eraser.
Also, just because you bought new batteries doesn't mean they're alive and kicking. Often, when you purchase batteries in bulk, it isn't uncommon that some or many of them are near dead or worse. Batteries bought in bulk tend to have a long turnover and such, can lose much of their battery power before they are used. And many batteries such as AAs are general purpose batteries and are not designed for the high energy use of digital cameras and the flashes they trigger. As such, I recommend using high energy batteries designed for digital photography. Varta is a good brand. They are usually sold in camera shops, are long lasting (because they are sold in small quantities) put out alot of energy.

At the very least, make sure you are using Alkalines.

Another angle to try, if you have an AC adapter, hook it up and see if the camera powers on. If not, you can eliminate the batteries and point directly to the camera itself.

With it's age and being way out of warranty, it may cost more to repair than it is really worth. The rule of thumb is that if the estimate for repair is north of 50% what you paid for it, you're better off taking that money and buying a newer and upgraded model.

the camera uses a lithium ion battery. i cleaned the contacts and still nothing. i even tried the ac adapter route and you guessed it... nothing.

Lithium's will die out. And if you could turn the camera on via the AC, I'd say pick up a new LiOn. But since you can't, it looks to me like it's time to get a new camera cause I just don't think it's worth the money to repair considering it's age. There are newer Nikon's out there which are better, and probably cheaper than what you paid for this one new.