the yellow (power; closest to the USB port) light staying on indicates that you are getting +5v power to the iDuino as you are supposed to. I am looking looking into a similar problem with mine. I have noticed that when the red light blinks, my MPGuino works perfectly, but when the red light doesn't blink, I have all kinds of problems. I am going to send Kevin (at Fundamental Logic) an email asking what the most likely source of the problem would be. At this point, I almost think I have a bad solder joint on the iDuino. I have found that tapping mine on a solid surface will sometimes make things work again, but that's not a fix, it's just a band-aid.
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