Check the battery, It should be over 3v on the red and black wires. The back pops off real easy with a small knife. either take the batter out and charge the battery manually for about 10 minutes, then re install, the power light should now turn white or buy a new battery . $25 on ebay.
New battery time. If the light just flashes yellow, it is because the lithium battery has dropped below its charging point. You can take it out and manually charge if with a 5 v supply for about 10 minutes, and put it back in. It should take off again. Or, change the battery. $25 on ebay