If it doesn't work at all in either mode, the likely culprit is a loss of 12v power to the circuit board. Does the control panel on the front light up and indicate Auto/Gas/AC?
If it works somewhat but does not get very cold, maybe 45-50 degrees instead of 35-38 degrees, then the possibilities are greater. There is a temperature sensor on the cooling fins at the back wall of the fridge and that may have gotten moved or its wire disconnected/broken. It could also be that the controller circuit board simply isn't responding to the temperature sensor. Or the cooling unit itself could have failed, though that would be rare on a 2005.
Is this a sudden problem or has it been getting worse for weeks or months?
Sorry to keep asking for details, but subtle symptoms are key to making a diagnosis.