Uhf but no vhf

I bought this tv about a year ago and just now am going to use it and I hooked it up to an external antenae, not cable, and I get uhf channels but no vhf channels. I get upper range channels, like 20-66, but I only get a blue screen when I try to get lower range channels, like 2-5-7-9, which are my local channels. The channel search does not grab them and they should be the strongest signal. Can you help?