in normal condition , Signal locked automatically, no remote button need for this.. In Rainy/cloudy season, Signal Unlocked automatically due to low signal count but when Restore to better signal quality , its again locked automatically.
but in ur case, may be either any of the 3 problem occurred I think.
1. may be a loose contact of wire connection from LNB. Please check that.
2.loose contact may be at Line IN port.
3. may be dust deposited on VC . Please do remove VC and clean the dust and Reinsert it.
and last but not the least., If u have any Spare HDMI/RGB cable please do check with the cable. Maybe HDMI cable is faulty (for Random Restart issue)