Yo, I've had the same problem with my Sapphire 2600XT. After, and only after I upgraded to XP SP3, standby mode was kaput. It would standby/shutdown, but upon rebooting it would just hang with a black screen; No BIOS, boot screen, nothin'. Perhaps you could risk downgrading to SP2 (at the cost of a few security updates) to see if the situation improves. I haven't bothered, as I'm going to update my 2600 anyway.