Only getting about 14 channels

Recently I have been having to unplug my receiver and plug it back in to get my programming.  It starts by channels having a black screen when changing to them.  Sometimes I can tune back to the previous channel but the reset is becoming a more frequent necessity.  Even more concerning is there are times when none of my HD channels work and only about 14 of my SD channels will work after the reset.  I can reset again and the issue may or may not resolve itself.  Any ideas?