Keg Carb Problem

[WrongCoastBrewery]

So I carbed a keg of beer about four weeks ago with about 4oz of priming sugar. It sat in a fermenting chamber at 68-70F for the entire time. I chilled it down to 40F last night and then tapped the keg this morning. Not one ounce of head and the beer was flat. Any thoughts on the problem?

 

[Yooper]

A very small leak around the lid? I'd try spraying some star-san around the lid and posts and give it a blast of co2. If the keg was airtight, it'd be carbed up.

 

[WrongCoastBrewery]

I leak check all my seals prior to and not one leak. I pressure checked it again at serving pressure (~10 psi) and not one leak.