Further things to try
1. Try running bare system with just CPU + Mobo + RAM + GPU(Either discrete or on-board whatever is available) + SMPS + Keyboard (You need to take the whole system out of your cabinet for the same and you should be familiar with such procedures) and check if you get the same error. Short the Power pins on the mobo front panel connector to start the system in such a case
2. If this time it works, may be cabinet assembly and mobo together has some issues.
3. If you still get the error, try reconnecting the CPU FAN again to the board
4. In your BIOS Set up CPU FAN Speed to full or disable automatic mode
5. Try fail safe and optimized defaults in BIOS try both the options one after the other and check if you still get the same error
6. If BIOS update is available try flashing the BIOS to latest version. This needs to be carefully done to avoid issues
7. Take a copy of the latest downloaded BIOS on USB/CD/DVD as a backup.I believe your Asus board should come with crash free BIOS that should offer a procedure to recover BIOS in case of any flashing corruption(Check mobo manual for details if being offered and how)
8. Re-Seat the CPU & RAM, in rare cases sometimes CPUs and RAM sticks misbehave