did you try restarting the computer with the camera plugged in? sometimes a restart is in order for a pc to recognize new hardware.
other than that, try going to Nikon's website. usually manufacturers have a troubleshooting section so you may find this is a common issue for this model.
also, using a card reader is better because when going direct you are using up the camera's battery. even though it has rechargeables, they only have so muany times that they can be recharged, no need to unnecessarily shorten it.
ps hope the camera's treatin ya well
