YES it is your led board I had same problem I refurbish armada e500s and the plug on the board breaks off if not properly installed look on ebay for that part pretty cheap like under $20 good luck.
I have a Compaq Armada E500 that must be unplugged and plugged into the wall to powerup. If I push the slider bar it will not work.
I have a fully charged battery, and it does not power up with or without the battery.
I've removed the floppy and cdrom with the same result.
I had thought it might be the Voltage regulator board, but had replaced that along with a motherboard/cpu upgrade and the problem remains.
I think it may be the Power LED board, but if anyone has any experience with this type of problem, I would appreciate it.