Basically, if you unplug
everything and clear the CMOS [with teh mains disconnected, etc] and then just plug in the mobo power connectors - not even the VGA card or it's power - then it should beep at you to tell you that you have no CPU/RAM/VGA installed. You can check the manual to see what beeps mean what but TBH you don't need to know until you can't think what else to plug in
The idea is you add components one at a time until the problem recurs.
So if you get beeps with nowt in, pop in the CPU.
If you still get beeps, pop in the RAM.
if you still get beeps, pop in the VGA and it's power connectors.
You shouldn't get POST beeps after that - you should get a display, and the next message would be from teh BIOS itself, really, either obviously being corrupt, or stating that an OC has failed [a bit of a generic catch all term for 'I'm lost and confused' for BIOSs]. If you still get beeps after getting to teh stage of adding the VGA card and it's power connector, then check the mobo manual to decipher the beep code and see what it points to.
If you get no beep with nothing but mobo power hooked up, then it's either the mobo or the power supply that's gone - only way to be sure is to plug in [and risk popping, if it's a broken mobo...] another power supply and continue.
If you get no beeps at one of the inbetween stages - say, plugging in some RAM, then you know it's possibly iffy RAM - check the beep code in the manual, and check it in another system if possible.
Repeat till fixed, or till you are chewing your fingers off in apoplectic rage at how rubbish computer components can be, something which I have
never done, oh no....