Could be a failing PSU.
Things to try first:
clear the CMOS or load defaults, check the CMOS battery, flash the BIOS.
If problem persists then strip it back to one RAM stick and the CPU then see if it POSTS. If it does then fit the graphics card and try again, if OK then install the SSD and try a boot. If it boots then progressively add back all the other peripherals testing as you go.
If it fails at any point then it could either be what you have just added or the PSU failing due to the increased load.
Alternatively replace the PSU anyway as its always useful to have a spare as its a quick way of eliminating it in the future.