2001 grand cherokee limited won't stay running

It rained two weeks ago and my 2001 jeep grand cherokee would not start up and stay running. when it was running when it started raining i noticed that all the gauges were not working. I let it sit for two days while waiting for my check in the mail, went out to try it and it started fine - the only gauge not working when it came back was the outside temperature overhead. It ran great for two weeks until the next rain storm came.
Now when i start the car it turns over and runs for about 3 or 4 seconds and then dies. Also i have noticed that the fuel, battery oil gauges are not working. I have checked the fuel pump relays and they are working, also the fuel pump is working. i am suspecting that the PCM is the problem. Is there a way to check?

Also could it have anything to do with my heater core going out, right before it began to have problems the car had overheated and i noticed the passenger floor was soaked.

And one last thing when either attempting to start the vehicle or stopping it, and even when just turning the ignition on to listen to the radio a weird noise starts and lasts about 30 seconds which sounds like the airbag... what is that

Thankyou in advance for your assistance

Was the leaking heater core repaired and coolant level corrected? Have you checked the battery cables? I would clean any connections that have coolant spilled on them. Get a loaner pressure tester pump system to around 14 psi with the engine running is the gauge pulsating if it is you have a bad head gasket.