Just randomly stumbled back into this forum, noticed a fellow gamer in distress
Firstly try booting up without any HDD's connected, If something happens, you will need to reset the BIOS to default (which should now hopefully appear, normally hit F5 or F8 to get to it when booting)
If that isn't the case or it did not work, next step is clearing the Bios CC, which is done by finding the small jumper pin on your motherboard (it's a 3 pin jumper with a small connector over 2 pins) It will be labeled CLEAR, CLEARCMOS, CC, CLR, PWD, PASSWORD, or something to that effect. you need to change the small connector on that over to the other pins (the middle pin and the currently exposed pin) then boot up the PC.
The PC will then make a beep sound (most likely, it varies) so after about 5 seconds turn off the PC, then move the connector back to the original poisition and start up the PC again, it should load you into the BIOS settings, which will be default, you will need to make sure they are ok, ie it recognises your hardware.
If that worked, awesome!
If not, I'd get your PSU checked first, sometimes single power rails can short so you think it's fine but it isn't, it's a real simple test you can take to almost any PC shop, PC world probably do it too.
If your PSU is fine, then yes, it does seem more likely that it's your motherboard, you could get your PC tested somewhere but that, unlike the other steps, will cost you money (but may save you money if you try and replace the bit that isn't broken!)
A little tip, for PC's, ALWAYS connect them to a reliable surge protector and NEVER connect devices to it that drain mass amount of watts, ie, toasters, guitar amps, hairdryers, electric razors, laptop chargers etc.
In fact, it will help your PC if all you connect is your PC (and maybe monitor(s)).