For the benifit of anyone with a similar issue here is Asus's suggestion to try. I'll be doing this tonight.
In this case I recommend you make a CMOS reset of the BIOS by taking out the CMOS battery for 3-5 minutes while the PSU is unplugged. While the power cord from the PSU is still unplugged, press the power button down for 30 seconds to power discharge the unit. Then place the CMOS battery back in, plug in the PSU and try again.
After this go into the BIOS > Advanced Menu > APM Configuration, from here set the ERP Ready to Enabled S4 + S5 or Enabled S5 and set the Restore AC Power Loss to Last State and test the motherboard again.