prusa i3 power supply

Hi lads and lady's, I have just finished building th i3 printer. But had laptop plugged into it and had the screen illuminated on the display panel. Now the problem I turned mains supply on on and there was a snap crackle pop! What have I done and how do I fix it?

 

What's a limit switch look like? I'm more used to working with wood not electrics

 

Here are some pics, excuse the mess just trying to get it going then I will tidy the wiring.
Blue running to negative and brown positive.