System was working fine. Just took it out and dusted out the guts - buttoned it back up and now it does that pulsing light, fan thing. Already tried reseating the connectors and boards - checked open sockets to see if some dust got in them - redusted - still same problem. No boot, no nothing... just pulsing light and fan. bTw... light on motherboard flickers. Never saw that before. Thanks in advance for your help.