I'm having the same exact problem as you, using the Radeon HD 6570 though. I thought it was a faulty motherboard but when I got the second one a week later it still never posted. Don't send yours back, that is for sure.
define not getting video. Do you never see it, as in don't see the post screen, or is that the last thing you see?
not sure what bios you have, but you need the latest (1605) to use an FX processor, which would fail after the post. Do you hear the hard drive working after the post, and maybe the windows sound as the desktop launches?
couple other things
Is this a fresh install? If not, is this the hard drive and windows install off the intel mb? If your HD is formatted IDE and the m5 is set to default hd config (ahci), the computer will give a short BSOD and reboot as windows starts.
did you switch brands of video card before the fail. you often need to uninstall amd drivers before rebooting to nvidia cards and vice versa
did you try booting single video card?
No, just a "No Signal" the entire time after power is started. I'm using the old HD from my intel board, and planned on doing a fresh install on an SDD, but I can't get anything to show. And no beeps or anything... I was using SLI, but I discovered it doesnt support SLI apparently, so I switched back to a single card.
well, it's not even posting, so video is not the issue. As you found out this MB is crossfire only, as is my m5a97 rev1
first, make sure the memory is ok. The red led should flash or come on for a short time when power is first applied, then go out. If it stays on, press and hold the memOK button on the motherboard, info in the manual on it. If that doesn't work, take out all cards, including the video and try booting. next, remove the memory and try it. What we are looking for is the point of failure. If you have nothing when you take the memory out, take out the processor. BTW, first check to see the green LED is on near the SATA plugs. This lets you know the MB has proper power and is ready to come on. If its out, then power supply is the issue. It may be good, but not compatible. dont forget there is an 8 pin connector at the top of the board in addition to the 24 pin. OH, while you are at it, make sure the clear CMOS jumper isn't in the clear position.
depends on how long you had it. check the policy of the place you bought it from. Most places like newegg give you 30 days to return and/or exchange, no questions asked. Some items are exchange only. After that, it's warranty with the manufacturer. Asus has a 3 year warranty, the details are in the manual, their website, or linked to off of the product page on newegg or wherever.