I have tested the fast boot on 8 Series board and it was working just fine for me. I recommend you updating the bios to the latest one on your unit by accessing the following link:
You can also try clearing the cmos on the motherboard by removing the battery for about 20-30 minutes while having all other components disconnected.
Im having a somewhat similar issue
My DH87RL motherboard will auto restart by itself when I select shutdown via Windows 7.
This is with and without "Fast Boot" from the bios.
In Fact, once i plug in the power cord it starts by itself, even when the switch connected to the motherboard is disconnected.
Is there a possibility for you to test a different power supply?
Please update the BIOS in your system to the latest. Here is the download:
before doing this i had updated to the newest update BIOS with same results.
my Issue was having the mSATA hard drive in the motherboard slot i used 2 different ones with the same results.
Bought this boards specifically for the use of mSATA and now im using it with an adapter, defeats the whole purpose, but at least is working.
so I found a Solution for my Issue, YES. but the purpose of the board is Useless I suppose.
I hope there is a fix for this. =S