Cobra computer troubles

Hi all, i have a Sunnto Cobra air integrated computer and am stumped. i have read the manual a couple times now and the problem is i cant get the computer to go into dive mode. i go air on turn the computer on get in the water and nothing happens. even after getting down to 15' nothing happens. i dunno what the deal is. anyone can help?
thanks Jon

Take it for service. There's something wrong with it; it should turn on automatically when the water contacts are activated.

Jon, is it the Cobra 1, 2, or 3? Did you buy it new? How old is it?
Do you get the "AC" message in the top right hand corner of the screen when underwater with it (or even if it is in a bucket of water)? Seeing "AC" means the water-activating contacts are working properly. If you don't get the "AC" then the computer's contacts (on the back) may be dirty preventing in-water activation and access to "dive mode".
Try taking an old toothbrush, some clean water, and give the contacts on the back a good cleaning. Towel dry, let air dry, then retest for activation. [check your instruction manual -- heading "AC Water Contacts"]

Also, if the Dive mode is set to "off" .... well then, you have to set the dive mode to either "Air" or "Nitrox" to get access to the dive functions [check your instruction manual -- heading "Accessing Dive Mode"]

Failing that, take the device to Howie at Frank White's on Blanshard Street (corner of Fisgard and Blanshard) and ask him to test it.
Good luck!!

thanks for the advice, its the cobra 1 with QD. i purchased it from dive and sea sports in newwest and it was one of george's staffs computer that upgraded to wireless. i do get the AC come up in water and thats why im so confused. i didnt know the dive mode could be set to off. i need to check that. i think i am heading to Victoria tomorrow from Pender and may just try to stop by Franks.
thanks again

One of my rental Suuntos is currently in the repair facility for the same reason. I can adjust all the settings on land, but it won't dive--just shows AC during the dive. There's no repair for it that a user can do, but the service tech can take care of it. It's not an unheard of issue, though it's also not hugely common.