Definately take it to an EXPERIENCED herp vet, like ozz said. If you don't know one already, try to get some references in your area, as many vets who treat herps don't really know them and can do more harm than good.
Firstly, frillies are notorious for going through "sulking" periods where they will become inactive, wont eat, etc. Mine has done this when I've moved cages, location of the cage, etc. Two weeks seems on the long side for this type of sulking though, so there may be some other sort of underlying problem.
My first guess (keep in mind that without seeing the animal, set-up, etc., the best you will be able to get online is a guess at the problem... which is why it is imperative to get him to a herp vet) would be that a major contributor to the frillie's condition would be dehydration. More set-up info would help. What are the basking temps? What is the ambient temp, both hot and cold? What type of top is on the enclosure? If it is a screen top, DITCH THAT NOW. Screen tops can turn the cage in to an oven. As the heat source heats the cage from above, all of the moisture rises up and out of the cage with the heat. I would suggest picking up some cheap plexiglass, cutting it to size, and placing it on the top of the cage. Covering the screen with tinfoil is also a temporary fix.
With the new top on, start misting the cage. A lot of times frillies, and many arborial lizards for that matter, are difficult to get drinking from bowls. It is more natural for them to drink dropplets off of the glass and leaves and other objects in the cage. An air bubbler in the water dish may help coax it over to drink. You could also set up a drip, made out of airline tubing. Drip water down from some sort of reservoir on top of the cage in to a water bowl, much like you would drip acclimate a fish. Even though my frillie will readily drink from a water dish, it still prefers to lap water of the sides of the cage.
Make sure he quits force feeding the lizard. Reptiles can go for long periods of time without eating. Two weeks is well within their range, so it will not starve. When it is ready to eat it will eat on its own. Force feeding a lizard that is not ready to eat will often times cause more harm than good. If it's not eating, it is likely not eating because its body is incapable of metabolizing food at the moment. Force feeding can result in a gut full of undigestible food which, if it remains in long enough, can spoil and cause even more harm.
I'd also cover all sides of the cage. This will help to keep it from viewing any external stressors. You should refrain from handling too. Just leave him be.
Also, I would suggest losing the beardie. Mixing species is generally not a great idea. Each has different needs and mixing them will only cause unnecessary stress and will result in neither of the lizards needs being met completely. I would take the beardie out and put IT in another enclosure, not the other way around. This will help minimize stress on the frillie since it will remain in the home it has become accustomed to.
So, to reiterate this long post....
Get him to a QUALIFIED herp vet immediately
Keep him hydrated
Keep him in a high humidity enclosure
Keep cage covered
Don't handle
Make sure your buddy is not force feeding
Remove beardie from enclosure
Is a frilled dragon the same as Frilled lizard or is it something else entirely?
