1). Due to ECMG communication error you may get all channels blank. You need to check KMS whether running or not (if you using Irdeto )
Just start the KMS control center
As well the same process in Gospell CAS
Go to gospell CAS web interface -> Modules->ECMG -> Stop & Start
2). Either It could be happen when loss of satellite signal also. so make sure the source feed.