I almost always have to do a smc reset.
I have a 2009 Imac 24. Often when I come into my office and try to boot the computer its dead. I have loaded it up twice and took it to apple to have it returned to me because it always works fine when I get there. So I put 2 and 2 together and realized when it doesn't boot if I unhook everything for 10 mins and reconnect it boots up. Apple has offered for me to bring it back but its a long walk through the mall with a heavy iMac and I want to fix it if I can.
Is this a good question?