Computer black screen after powering on

This is a desktop. FX 8350 + AM3+ mb +2 4gp ram + R9 270 + 2 hard drives and 500W PSU. It was working fine before. Then one day, the screen is all black when I powering it up. At first, I can still see the hard drive led running and it seems like it is powering into windows. just no displace or even the start up screen. Just completely black the whole time. Then I unplug the CMOS battery to reset bios. Now the hard drive LED is not on either. All the fans are running. No error beeping. I tried:
1. replug the CMOS battery
2. Replace video card
3. replace motherboard
4. use only 1 RAM and use different slots
5. use different slots for video card
6. use different video cable (hdmi, vga)
None of them worked. I am ordering a new PSU but if that doesnt work, i really dont know whats going on now...