Do you have the automatic switch-over regulator? These have a transparent cap on the top that has a red/green popup inside the glass to tell you you have gas pressure in the selected tank. If the popup is showing red you are low on gas. If it is green you have gas pressure on the selected tank.
If you do, there should be a lever that is part of the regulator, and it needs to be pointed at the tank that is turned on and has gas in it.
The other possibility is that the tank safety POL valve has tripped. Try turning off the tank completely, waiting a few minutes, and turning the tank's valve back on VERY slowly...that might get gas to flow properly.
Two good ways to check for leaks: Use soapy water or store-bought gas leak detecting liquid and a brush to put the stuff on ALL fittings, look for bubbles.
Alternate is a portable, battery powered natural gas/propane sniffer tool from the big box store. Read and follow the instructions with the unit...
Another issue may be that you have a LOT of air in the lines, so go to the stove, use a BBQ butane lighter, and turn a stovetop burner on with the BBQ lighter flame next to the burner. If the BBQ lighter flame blows around, you have air coming out. Wait for the gas to fill the lines, and it should ignite. Once it lights properly (blue, steady flame), try the other appliances. Be patient, you may still have some air trapped in the lines. Keep the doors and windows OPEN while you do this to help prevent propane from building up and igniting with a hell of a woosh--it's no fun to be front and center in a fireball...
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.