The two valves appear closed. Did you close the regulator, too?
With everything closed, you could make up some soapy water or standard strength Star San/water solution and paint or spray all of the connections from the keg on out, looking for bubbles.
If you rock the closed up keg a bit you can encourage the beer to out-gas some of the CO2 dissolved in it from primary fermentation, might help bring out the bubbles...
 I might have missed one or two, but there's like 16 joints there that have to be gas-tight. I don't think I have that many gas joints in my six faucet keezer