If the battery is completely flat the device may not charge.
Try leaving it on charge for 12 hours or so to see if it will charge.
If it still wont boot you will have to buy and external charger caddy to recharge the battery.

When the battery is fully charged and you can boot the device, follow instructions here to do a full reflash of your device and it will be like new.

If you can't reflash or charge (with your external charged battery) there maybe something wrong with the USB port. They are known to be easily damaged, if your not careful with it.