IT takes a week or two to dissolve CO2 in, without shaking/rolling/rhumba/foxtrotting the keg.
A couple hours is not enough, under static conditions (non shaking) to un-dissolve.
Take all pressure off, warm keg overnight, remove pressure again, chill keg overnight and then hook up 10psi.
Or search for the instant method here on the forum, which is turning keg upside down and blowing CO2 in while draing out line into bucket. But that will stir all sediment up. THere's another thread somewhere about hitting the side of hte keg with a rubber mallet also.