I have had this problem before but it went away after leaving my computer for a few days, it is happening again but won't boot into the OS. I have tried clearing the CMOS which didn't work? And I can't really return any of my components because of my location.
how old is the system/components you are currently running, could the capacitors have swollen? I see this all the time with Dell and HP repairs, I also see this regularly with older 3-4 year old PSU's on certain education systems, replacements usually fix the issue, might be worth getting a cheap tester psu to test your system board with, then slowly add components to see what fails.