The reason I asked about the light was if they don't get enough it can make the tom loose potency. If they are eating alot of corn that could be your problem. Corn is low in protien. You can raise the protein level and see what that does. Make they only eat the the feed you give them and you can get a couple bags of chick starter or better yet game bird starter. Chick is 20%, game bird is 28% protien. Mix that 50-50 with your layer pellets. Our you can boil back eggs and feed them that, some people feed cat food as well. Either way still give them the layer pellets, they need the calcium. If it's the feed you should get fertile eggs in about 2 weeks.
If that doesn't work it could be the tom himself.
Steve