Four things required for a POST (Power On Self Test)
Those are the only items needed in order to achieve a successful test of those components and get a POST "beep".
Yes, power it on with no memory installed. If it beeps, then the motherboard is responding.
plug it in turn it on and if it start making beeping sounds then it probably works.
no 100% way of knowing untill you get the parts though
Do you mean if the motherboard will turn on ?
Well just turn on your computer and if it opens won't any failure it will work
But if your computer won't turn on it's not working even without a OS your computer should turn on
add hard ware that you know works (processor, hard drive, memory) and see if it turns on. if it does not, use a known good power supply to see if it is the PS or the MOBO