CO2 tank empty in 4 days!!!

After getting my 5lb CO2 tank on Wed and set it and forget it carbing at 11psi, the tank is empty this morning. I know what they say about the cold dropping the needle on the gauge. But it is at Zero and the tank does not feel heavy at all. Its feels like the day I got it new from kegconnection.
What gives?

Sounds like you have a leak somewhere in your system, and the CO2 has gone the way of all things.

First question: is the beer in the keg carbed at all?

Then, for next time: Check all of the lines and connections for leaks once you hook it up. Seat the lid on the corny keg once you fill it by hitting it with 30PSI, then purge the oxygen. Spray some star-san onto the various fittings and check for any bubbles, which will indicate a leak.

All of these things you just may have to do once you've refilled your CO2 tank and plugged it back in.

If the high pressure guage shows empty, then most likely the tank is empty and you have a leak somewhere.
Remove the tank and check to see if there is any gas left in the tank. If the tank is empty, then you need to check all your connections with a soapy water mixture, when you get the tank refilled, to see where bubbling occurs. That would be your leak.

Even with the difference in pressure showing on your high pressure guage, it shouldn't show empty. If you have both a low pressure guage and a high pressure guage and only the low is empty it could be you have the gas turned off and the pressure was absorbed by the beer.

Some regulators have require a seal between the tank and regulator, make sure you have this installed. Also, use teflon plumbing tape on all of your threaded fittings. Finally, double check the seals on your keg, and make sure you have clamps tightened on your hoses.