Others have experienced the same or very similar symptoms as you described. You may want to follow the thread below and comment there as well...
I was able to resolve this particular symptom by ensuring that my external USB hard drive was not plugged in to the USB port. That's not really a solution, but rather, a temporary fix.
What was happening (apparently) was this...
Even though I had USB optimization disabled in the BIOS, the board was still attempting to reconcile the status of an external HDD on bootup. There seems to be some kind of timing issue, because it takes the Seagate Free Agent drive about 8 to 10 seconds to spin up from a dormant state, which is normal for the drive, but apparently not fast enough for the BIOS to resolve it's status. Apparently, the BIOS senses the HDDs presence, but it cannot reconcile its status because it hasn't spun up yet. Consequently, the BIOS was placing it in various sequences in the bootup list of priorities, even with USB optimization disabled, as well as the other USB boot option that facilitates not using USB devices during bootup.
Likewise, with the external HDD attached to the USB port, an error message on bootup would occur. I do not recall the exact wording of the message at this time, but it involved bootup failure due to an unrecognized or inaccessible device and began with "BIOS has detected previous POST attempts..."
Consequently, I now leave the external USB HDD unplugged until Windows finishes loading, then I plug it in and it is properly recognized about 8 to 10 secs later, which is normal for this particular drive.
This method is an annoyance, but at least it gives me full access to the F2 key on bootup which I did not have when it was plugged in. Also, there are now no error messages and no flashing LED power light after I boot up.
Hopefully, the SSDs will continue to drop in price and will completely replace all HDDs soon.
I suppose it's still possible that there is a specific configuration that will work so that I can keep the drive plugged in at all times, but I do not want to experiement with numerous combinations until I accidentally stumble upon the right one. I'll just unplug and plug each time until an official resolution is released.
I tried unplugging all usb cables - and still doesnt solve the blinking power light issues. The only thing I have plugged into the desktop is the monitor displayport cable, ethernet cable and tosllink audio cable and of course power plug The only way I could solve it is by turning off all fast boot options, but of course this prevents booting up faster.
On your issue try to change the boot order of your drives, go into the ADVANCE section of the bios, click to BOOT button then on the right side is a list of all your drives, move them around by clicking/dragging them up and down into the order you want them to boot. Put your usb drive to the bottom of the list.
Got the same problem with blinking power light on my Thermaltake Shark case with same motherboard and somehow i thought it was normal....Got some of the fast boot options myself and the Sleep mode trick did the trick.Please fix this little bug cause the motherboard so far is rock solid .
Thanks, Prakash. Yes, your solution was actually one of the initial actions that I tried, without success. The problem with my hardware is that the Seagate Free Agent external HDD goes into a dormant mode if the drive is not accessed periodically. Consequently, when booting up, the BIOS continously sees it as "new hardware" each time and it isn't sure where to place it in the sequence after it eventually recognizes that an external HDD is present. It senses its presence as new hardware each time, so even if I set it correctly in the list that you mentioned, the BIOS loses it the next time I boot up and the process starts all over again. I'll be replacing the drive soon, so I'm not overly concerned about it. It's just an annoyance for now.