"So i should check the BIOS to ensure the Sli is not running when I have the 4870x2 in?When I first installed the 4870X2, all I did was install the card, boot up and install the drivers and it went fine. It was only a couple of days later when he tried to boot up from cold and it didn't do anything besides the power light amber flashing.It does boot up every now and then but it's not booting up more often than it is.And the weird part is that it's still doing the same AFTER I put the 8600s back in.... "Hmm, if it works sometimes then it's propably not up to Bios settings, but you should still definately check them. And yeah I think SLi should be disabled when using a single Ati GPU if such an option exists, never had a crossfire/sli mobo myself so dunno how it is. Check the mootherboard manual if it says anything about it.
You could try the card in a different pci-e slot as well(and check the corresponding bios settings), not that it should matter if they're both x16s but worth a shot.
Unfortunately random boot up problems like that are often in fact related to the PSU, I've had a few give me trouble similar to that towards the end of their life cycle. I guess it could be that the 4870x2 was too much for the old PSU and it did permanent damage to it. But I'd still check everything before blowing more cash on a new one.