freeze the black screen

[sheffblade]

hi all after doing a format of my cam everything went ok did patch and new keys !!!!!! perfect or so i thought all channels opened on thor but every few minutes the screen freezes the goes black , after a minute or so it comes back on , have i done something wrong could it be my dish that has moved slightly ( bad winds in sunny sheffield the last few days) or i have done something more serious thank in advance martyn