Porter refusing to force carbonate woe

Can anyone help me with this. It's really frustrating. I am trying to force carbonate 19ltrs of a rather nice porter.

Temperature is 8 degrees
Pressure is 36psi/250kpa
Keg appears to be holding pressure fine
Gas tap IS open and there is CO2 in the bottle
Plenty of head space in the keg
Totally flat, no head, not over carbonated.
Never had a problem like this before.
Been in there for way over a week so it should be way way over carbonated but it is flat with hardly a hint of foam.

It has been in there for ages but it is refusing to carbonate!

Right, i have checked the keg isn't leaking for the third time and it isn't. There is the slightest hint of carbonation there, but hardly any. I have turned the CO2 up more in case there is something wrong with my gauge and turned the temp down to 5 degrees.

Corny Keg?  Pick it up and shake it.  I can force carbonate a beer in 20 min by pressurizing and shaking and repeating the process.

I also love my stainless steel carbonation stone.  Just never make root beer for the kids with it.  It soaked the sarsparilla and I can't get it out!

There HAS to be a leak, or something.  Either that, or your keezer is a link to an alternate universe where physics is different. 

At least there's still beer in this universe, but I digress......

A buddy is a C02 guy by profession, and taught me a trick.  Do you have a shutoff valve?  Like a ball valve that you can flip on/off easily?

If yes, flip it off.  Wait a few seconds.  Turn it back on.  If the needle jumps, start checking connections, something's leaking.  Not a slight wiggle mind you, that's normal.  It'll jump a notch or two.  You'll know.

Right, we're on. After two days of stupidly high pressure my porter is now carbonated. cheers for your input! Been a help.

Never really quite got the hang of force carbonating. It's is always too much or not enough. Can anyone give me a run down of their method; temp, pressure etc.

Cheers

I had one that seemed to take wuite a while to carbonate and I think it was because I forgot to purge the air.  I think the air kept the co2 from getting to the beer.
I normally turn mine up to about 30 psi for a couple of days then run it at 12 to 14 and leave it alone for two weeks and see how it is doing. Usually its done after about 3 weeks  This is much easier if I have another batch that is ready to drink.