|im thinking its a dead or rather dying PSU or certain components are not getting enough power. but usally you get through post and begin startup.|
fist the simple things: try plug-in the tower into a wall socket on its own i.e. not via a multi extension.
do you have another power cable available - to be fair if it is the cable then it shouldn't do anything.
try removing everything that isnt essential. start with usb devices and any secondary hdd's dvd drives etc. so that your left with the bare minim.
i am unsure if your comfy with doing this as you comment regarding connections can either mean youve checked your mobo connections or you just mean the power cable into the pc. if you mean the latter then please say so i dont want to give you brief advice for something your not comfy with and you go tinkering with things and risk messing things up further when it could be something simple(ish).