communication timeout after powering up
I bought a new arduino mega 2560 with ramps 1,4, uploaded firmware that worked on last one and all worked, then I used new (tested with multimeter) 12V power supply. From that time everytime I try to connect to computer it only blinks and repetier-host says communication timeout. I tried reuploading firmware, but arduino IDE says the same... communication timeout. I tried reinstaling driver, also alternative drivers for this type of board, but same. I tried all other baud rate setting, but same. And I tried this all on two separate computers (one have got Win10, other one Win8.1) Please what else can I even try? Or how can I avoid this to happen next time?