I have an XFX 680i LT, and up until a few days ago it had been fine for a year. My computer starts up, but there is no signal to my monitor. I did a graphics card swap, memory swap, hard drive swap, and CPU swap, but nothing worked. My power supply is working, otherwise there would be no power to my computer when there is. I didn't think it was my motherboard because the onboard fans and my CPU fan have power, but at this point that's the only piece of hardware left that could be causing a problem. Is it my motherboard or something else?
My friend JUST had the EXACT same problem and we went through almost the EXACT steps you did (but we didn't have a hard drive or cpu to swap, however we did swap PSU). The fans would spin and LEDs lit up, but there was no signal to the monitor. We tried clearing CMOS, letting it sit up for up to 15 minutes (didn't have the patience for any longer haha, the 15 minute wait killed us) and eventually went to Fry's and got a new mobo.
Oddly enough, THAT mobo was bad too, but once we returned that mobo to Fry's (which turned out to have a bent pin on the CPU socket) and plugged in the second replacement mobo, everything booted fine.
So yes, it's most likely your motherboard. Check your CPU pins and see if any are bent.