Most likely a bad connection at or close to the antenna. If at any time water has gotten into the coax then replace the coax.
Or the coax has just gone bad , Replace to coax on the outside.
All so replace the matching transformer (balun) if one is connected.
Aim the antenna at about 327 degree magnetic compass.
Here is how to aim antennas ,
http://www.kyes.com/antenna/pointing/pointing.html.
For a new antenna install a HD7698P aimed at about 327 degree magnetic compass.
The HD7698P antenna is a large antenna and as such will receive the most Tv stations.
A amplifier will most likely not be required.
http://www.solidsignal.com ,
http://www.winegarddirect.com ,
http://www.amazon.com.
Here are some STRONG and STURDY antenna mounts ,
http://www.ronard.com/909911.html ,
http://www.ronard.com/34424560.html ,
http://www.ronard.com/ychim.html ,
http://www.ronard.com.
Buy the ronard mounts at solidsignal by typing the word ronard in the sloidsignal search box or buy from ronard.