Luckily, all a PC needs to boot into the BIOS is a PSU, a motherboard (with CPU and RAM) connected to a monitor. If the motherboard doesn't have video processor is needed also, but that complicates things.
So disconnect the SSD and the 2 hard drives, and if possible the video card and try again. If that fails, you know that the PSU, the motherboard, the CPU or the RAM is defective. Then replace what's broken.
We recommend to take everything out of the case to prevent short circuiting when experimenting.
I was having this problem before I upgraded In April but it wasn't that bad and thought I sorted it as didn't do it for a long time but after I got my upgrade case and graphics card all seem fine for a few mouths and only resently it started doing it again but this time it didn't post at all powered on you hurd all the fans were going as they normally do but no post and saw no lights on inside as normaly the graphics card lights up so troubleshooted to the motherboard toke out every thing but 1 stick of ram and cpu and still no post a friend had a motherboard he wasn't using so let me try that fitted it and all seemed OK on first boot up after shut down then coming back to it turned on and same thing getting no post really need help in working out what's wrong also tyred taking out hard drives and still no post thanks in advance
8gb ddr3 ram
GTX 1060 G1 6gb
250gb Kingston ssd
2x 1tb hard drive