Hi Michelle,
This sounds as if it might possibly be a problem with buttons. If so, it is easy to fix and Atomic can either send new buttons or take care of it for you through service/ warranty. But first, how old is your Cobalt, and is it a Cobalt 1 or 2? If you can give the serial number and firmware version that will help narrow down the issue. Some of the older Cobalts had button magnets that were not as well sealed as in the recent models. I will message you here on SB with instruction on how to check the keypad.
It is normal for the Cobalt to wake to the dive screen on contact with water, but just pressing the select button should put you back in the screen that you were in when the computer went to sleep. Is it possible something is shorting the pins under the Cobalt's nose, or that they are wet?
If you press the Select button again, does the set compass bearing dialog come up?
If this is a Cobalt 2, pressing the Select and Back buttons together for 11 seconds should reset the system (you will need to set the time and date if you do this). But if your back button is not functioning this won't work.
Updating firmware is always a good idea, but this deems most likely a button problem.
Ron