You need to clear your cmos.
From page 17 in your mobo user manual:
Note: CLRCMOS1 allows you to clear the data in CMOS. The data in CMOS includes
system setup information such as system password, date, time, and system
setup parameters. To clear and reset the system parameters to default setup,
please turn off the computer and unplug the power cord from the power
supply. After waiting for 15 seconds, use a jumper cap to short pin2 and pin3
on CLRCMOS1 for 5 seconds. However, please do not clear the CMOS right
after you update the BIOS. If you need to clear the CMOS when you just finish
updating the BIOS, you must boot up the system first, and then shut it down
before you do the clear-CMOS action.
Page 10 shows where the CLRCMOS jumper pins are located on your motherboard.
Don't disable legacy USB support