Try switching the receiver off from the back for a couple of minutes. If that doesn't work, bring your dish inside the house, it might be too windy out there, causing signal disturbance.
Tom, try doing a factory reset on your recevier. With the power off hold the channel-up button while pressing the power-on button. You will get a menu. Select "NVram clear". Make sure to write down all of your receiver settings before you do the reset, as you will loose them.