To get Echo 7 and Echo 3 you need two dishes and a switch. If you have these, look at the Antenna setup and see what disEqC switch port your Echo 3 is connected to. Then look at Echo 7 and see what it is connected to, and connect it to any port other than where Echo 3 is connected, but where you have signal. Then do a blind scan (power scan).
If you post again, please make sure, you give details of Dishes, LNBs, switches and current software. Without details it is not possible to help.
Try DisEqC port 1 for Echo 7. Normally Port 1 = Echo 7 Port 2 = Echo 8.1 Do a Power Scan (Blind Scan)
Did you at all do any disconnect/connect? In the past, did you ever get both Echo 7 and Echo 8.1? Any way, if you do any connect/disconnect of antenna cable, keep the receiver main switch off.
If Good number of channels on DisEqC Port 3 and nothing at all on Port 1 and Port 2 and Port 4, there may be to be a disconnect of the cable to the switch or a deffective LNB