can you get into bios ? if not use one stick of ram see if it boots if not change to the 2 and see if it boots keep doing that until all are checked .
do you have something new you just put in ,pull everything extra, do you have a video card or is it built in ?if so pull it out and if possible change to different video card.
after everything else I don't know if you've ever done this but after years of use most cpus have to reapply thermal paste but if you have never done this please get help.
last ditch the mother board could have gone bad hope not . if that happens time to upgrade or buy new. you never really said what system is so can't really tell what you have there
not sure this will help.