Kegged Beer Flat after 2 weeks

Kegged (for the first time) a brown ale from extract with specialty grains, using about 1/3 cup of corn sugar in the keg, sealing it with CO2, and letting it sit at room temp for 2 weeks. Put the gas on it this afternoon, and while it isn't chilled, I pulled 2 glasses to check on clarity. The second glass was very clear, real foamy head, but no carbonation in the beer itself.
Any suggestions? I assume it'll carb up by force since I've got 10 lbs on it in the fridge, but I was surprised that it was so flat. Before I turned on the gas I did burp the relief valve and there was plenty of gas in the keg, so it apparently didn't leak out over the past 2 weeks.

Sooooo you let the beer carbonate naturally for 2 weeks, then pulled the relief valve, releasing the co2 created, and its flat?

Just like a bottle I would suspect you would need to chill the beer for several days to get the CO2 into solution. Just like if you don't chill a bottle it will foam over and leave you with relatively flat beer.

Well, nuts. I didn't think a quick burp would make a full keg go COMPLETELY flat that quick, especially since the gas was put right on it which I would think would prevent any subsequent loss from what was in solution. Ah, well, live and learn.

If it's been at room temperature, you're going to need to have it at over 20PSI in order to achieve typical ale carbonation. Also, refrigerating it will force the CO2 to absorb into the beer, and requires substantially less pressure. Once it has a chance to stabilize temperature and pressure over a couple of days, it will continue to condition, carbonate, and will likely clear. Just give it time.

Well, it's in the keg at 45 degrees as of this morning. I'll leave it sit a few days. The glass I pulled and drank last night was absolutely clear. The first glass I pulled I tossed.