i wouldnt use cat food,...its made for cats.
try soaking bearded dragon pellets and dripping the mush on his nose with a needleless syringe if u cant get him to eat the bugs, they will sustain him till u can work out whats wrong or get him to eat his crickets, you can also blend up cricks and veges into the mush to make it healthier fro him
if hes new he might be stressed which puts them off eating.
another thought is the temps might be wrong.
low temps will cause digestion problems which lead to lack of appetite (and impactions), basking spot should be 38-42C measured with a digital probe thermometer fro accuracy,,....
a warm bath (not hot) will help with hydration incase hes dehydrated, mist him with a spray bottle while hes in the bath, dont mist him in the tank cos damp tanks lead to respritory infections,...
does he have a UVB light? no UVB light will also affect thier activity levels and appetite,....