Heating bed causes RAMPS to overheat and cut power

Okay, this one is puzzling me. Basically, I'm building my prusa i3, and I start up again working after waiting a week for a new hot end to arrive. But when I try to run a job, The bed never gets past 40 C. A bit of rummaging about the internet later, I noticed that the red light on the board was going off when the bed stopped heating up, leading me to conclude that the board was overheating as several otehr forum topics discussed. However, they didn't list a solution. I tried adding a fan to the electronics to keep it cool, but that didn't help. For some reason, further, now it only goes up to 30C. I'm at a loss. Any suggestions?

scratch that 30C part, I tried to show the issue to a friend and now the bed won't heat at all.

couple off pics of the heatbed and ramps " solder side" assuming it is a ramp may help , quick test " once you checked the wiring for a hair short" wire it too D9 and use m106 s200 in pronteface if you get past 55c turn it off it proves the fet on D8 gone bad ,,either replace the ramps/fet or set the bed in firmware to use D9 in firmware this method would mean you have no fan!!.

yeah, so... Thanks for the advice. Once I figured out what you were trying to say, I tried it. You seriously need to use punctuation. and grammar. But your suggestion did set me off on another path. While investigating the MOSFETs, I noticed that the larger of the two polyfuses had a crack running down the side. I replaced it and plugged everything in again, and now the bed gets up to temp just fine. Thanks!

I have heard that the polyfuses (?) on chinese boards aren't always up to spec and that some individuals just replace them with fuses from an auto shop.

Glad it is working for you.