Nimbus

Okay here's my situation. I just installed an activated Voom receiver that I bought on eBay. I attached it to a Phillips 45db amplified antenna. I live 35 miles from the stations. My zip code is 27712 in Durham, North Carolina. Anyway I just hooked it up and I can see all the local channels but they keep cutting out. It gets all pixelated and the screen keeps saying "No signal received on local channel 5-1. Check Your Signal." I pointed the antenna in the direction of the towers but nothing seems to help. I was under the impression that once it grab a signal it would just "lock on" to it?

Is my problem with the antenna? Should I try and get one of those silver sensor antenna's? Or go for an outdoor antenna? I would prefer something indoors since that would be easiest. Based on the message I'm getting it seems like the antenna isn't strong enough or something.
Any help would be greatly appreciated. Thanks.