WOL (Wake on LAN) issue

Hi,

I have a room full of workstations that sometimes the WOL works and sometimes not. 

My conclusions from the tests I made are that if the NIC have blinking lights and I send the WOL packet it will boot. But maybe in the next boot, without changing nothing, if the NIC stays with led turned off when I send the WOL packet it does nothing...

I've update BIOS, UEFI, etc and nothing worked! 

Thanks for the help!