I've got some D.C power supply connected to my breadboard, and there is definitely current going through it as I've put some resistors in series and parallel and checked the values on the multimeter vs my calculations and it seems to be alright. Now I put in a 5mm LED in series with a 100 ohm resistor with 3 V and it didn't light up, I tried different combinations making sure that the calculated current didn't go too high, but I couldn't get the LED to light up and I know it was working because I tested it at the store before I bought them. I looked at the power supply box and it says it outputs 2.5A max, does this mean that 2.5A of current was running around in the circuit and possibly damaged the LED? I don't want to test out the other LED's until I'm sure of what's happening. The multimeter has two connection options, for currents less than 200mA and for currents over 200mA, and I can only seem to get a reading when the currents over 200mA option is used. Edit: Tested the LED with the multimeter diode test, and it lighted up, it's a blue LED, so the LED is definitely working, but just not in the circuit.