(edit) Whoops, just saw a thread from a couple of days earlier - I forgot the most obvious thing!! You may have the wire connector going to the mobo reversed (or the LED is plugged in reverse) !! You gotta have the correct polarity to the LED for it to work! If you are sure you have the LED connected correctly, then continue reading; if you ghave it reversed - fix it!
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I have an Evercase 4252 sitting on my bench and I just checked out the Power LED mounting situation. Pretty easy to change when the case is empty; filled it will be a b*tch! LED is not soldered in. Remove the Switch/Light holder assembly from the case; pop the 4 vertical tabs on the front of the metal case (bezel removed) then cut the zip-tie that holds the wires to the front of the the case fan punchouts and then remove the whole d*mned thing from the case. Once you have the white plastic Switch/LED holder out where you can see how it is put together, pull/slide the small square LED holder (at the top of the assembly) out of the 'holder'. The LED is plugged into the small, square 'thingy'; it is only held in by the folded over piece of silver colored 'lead' sticking out (and friction of the leads and the wire terminals)! Unfold the bent over lead and slide the LED out of there. Just about any 2.1 volt to 5 volt LED should work OK - the color you choose determines what voltage you get/end up with. The mobo supplies +5vdc (everyone I have ever actually measured) to the LEDs. Cut the leads on a new LED to match the old one and reverse the aforementioned process to reassemble! Just remember that the white wire is negative; the LED cathode (or negative) is the shorter of the two leads. The 'tron god favors the cathode being connected to negative potential (coversely the anode goes to positive, green) OR it ain't gonna light up !!!
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