Start with a proper Clear CMOS, unplug the PSU for 5 minutes then move the CMOS Jumper for 5+ seconds and then back again, plug the PSU in and try again; see - http://www.youtube.com/watch?v=rdHH9KrceR0
If it posts then for now boot into the BIOS press F5 (Load Optimized Defaults) and F10 Save & Exit = yes.
If the PC is still stuck in some form of Standby then hold the Power switch for 5-10 seconds or if needed the Reset button. If the LED still gets stuck on 'red' then I'd re-seat both the 24-pin & 8-pin from the PSU.
Let me know.