The Arduino is probably fine. I would concentrate on debugging the RAMPS connections: 1. Check your power supply first by connecting the heated build plate directly to the power supply (> 11 amp line). If the power supply is legit, I assume the build plate would heat up. 2. A separate power line (>5 amp) is needed to power the extruder/motors. This should be a 12V line. 3. The wiki mentionby verticalData - General Mendel Topics