bed and hotends sucking power from each other

Hello! i'm building my first 3d printer, witch is also my first arduino project, so i am pretty new when it comes to all the electrical stuff. The first time i tried to heat up the bed in pronterface, just for testing purposes, the mosfet started smoking and slightly melted the blue connectors(now i know its a standard fault with ramps). I changed the mosfet and added heatsinks and fans to keep them cool. But now, for some reason, the bed and two hotends act like one big heater: if i set hotend 1 to heat up to 100 both hotends heat up to 100 and stay there, and the bed also starts to heat up slowly If i set the bed to 70 the hotends start heating incontrolably and end up at >350 and climbing at witch point i would just pull the plug. The wiring is wright. But i have no idea that the hell is happening )). It's been about 5 months since i started this project and i would love to print without setting the house on fire. Any ideas are more than welcome.

Fixed it! Turns out it was my lack of knowledge in electrical engineering. It just so happened that i was looking at a PC motherboard today, when i noticed that all the MOSFETs where laying flat and the drain whas not connect to the board, buuuut, the tip of the MOSFET, where you would screw in the heatsink, was soldered to the board. Five seconds of googling later i found out that the tip also acts as a drain. And the heatsinks i mounted all touched each other because they are a bit oversized, out of my fear of the board catching fire. I knew that ramps 1.6 has a big heatsink that goes across all three MOSFETs, so i didn't think it would be a problem if they touched. I now realize that in that deign the MOSFETs are laying flat o the board so the heatsink only touches the plastic bit. Long story short, a big of insulation in between the heatsinks and evetrithing looks like it's working.