One video card not recognized

[SLI AMD 24]

I have a problem with one of my video cards. I have 2 MSI 7800GTX cards 256MB. Sometimes on boot up only one gets recognized and sometimes its both. I don't know if it's a driver issue somewhere or what and I'm not sure why. I keep my machine on all the time now so I don't have to deal with it, but I'm goign to have to reboot sometime and don't wish to deal with this anymore. Does anyone have any suggestions?

 

[NoxTek]

What brand and model of power supply do you have?

 

[SLI AMD 24]

500 W X-Connect I believe It is a modular power supply. I have been considering the Hiper 580W if it's necessary. I'm running a watercooled case, the 2 7800 GTXs, 5 SATA drives, 2 cd/dvd burner drives, either my floppy drive OR my Audigy 2 front panel (depending on the use needed), and 2 cold cathode tubes though they are rarely on. I've been looking to find out the limits of the power supplies but havne't had a lot of luck on it yet.