98 Nissan Maxima – Computer Trouble

I am not sure if my problem relates specifically to the dash or if it a bigger issue with the cars computer. Yesterday, the gas and temperature needles rose all the way to full and hot, the speedometer stopped moving altogether and the rpm needle started bouncing erratically. (The gauges on the dash are all needles, except for the trip set and odometer which are digital… the trip sets seem to be correct, but the odometer is reading 9999999) I drove the car and everything was operating normally except for the gauges and I am unsure as to whether there is a problem with the instrument panel or the cars computer.

I disconnected the battery for about an hour and then upon reconnecting, all had returned to normal… This lasted for about 2 short drives and now the dash is behaving in the same fashion.

I am unsure as to what troubleshooting steps to take at this point and was wondering if anyone had any experience solving any similar problem.

Also, if I need to change the computer, does anyone know if this is a big deal… or easy to do?