Hello. The description of the blinking yellow LED at the B spot indicates an issue with either the power supply unit, UPS, PDU, power cables or system board. Try re-seating the power cords and if no change use another known working power supply.
My PowerEdge SC1420 will not power up.  The power button blinks and the yellow light is on at the B spot.  Does anybody know what the issue is?
PowerEdge 1420 not powering up