hi, have you tried him on hoppers/locusts (sorry i'm from london and we call 'em hoppers) my beardies love them. They will eat crickets but only when there's no choice, and then they will not touch black crickets only brown ones. Does he eat veggies ? if he does try putting the crickets in with the veg and he might eat some by accident. If he doesn't eat for more than 48 - 72 hours and he hasn't pooed it may be worth contacting a vet as it may suggest impaction (serious constipation). If he hasn't pooed in a few days try giving him a warm bath (have the water about 80-85 fahrenheit, same as his tank). This will encourage him to poo, which will in turn encourage him to eat.
Keep a close eye on him, if you are in doubt, go to the vet, I've seen a beloved beardy die cos I thought a couple more days wouldn't hurt ! Never Again.
I hope he is well, good luck dude.
Ed