Please update the latest BIOS from ASRock official website firstly.
Download link: http://www.asrock.com/support/download.asp?cat=BIOS

Because of AM4 memory compatibility issue, some high frequency memory modules may not work with XMP profile successfully. ASRock keeps updating the latest AMD AGESA code to enhance the high frequency memory capability. Please keep tracking the latest BIOS update on ASRock official website.

We have tested some memory modules on AM4 platform and users can refer to our suggested module list for choosing the finest ones to pair with your AM4 motherboard.

Memory support list link: 

X370 Professional Gaming , X370 Taichi , X370 Killer SLI/ac , X370 Killer SLI ,
X370 Gaming K4 , AB350 Pro4 , AB350M Pro4 , AB350 Gaming K4

M.2 specification support may vary with a different AM4 motherboard. Please refer to the following table for support information.

Please refer to the following table for detail information.

Please download ASRock RGB LED Utility from the following link, and the LED can be controlled under OS.
Link: https://download.asrock.com/Utility/Others/RGBLED(v1.0.12).zip

Normally, the boot time for AM4 series motherboards is around 30-45 seconds.
Boot time may be longer if clearing CMOS or boot up from getting AC power firstly.

Please refer to the following table for the fan type specification and information.

*Auto detect – system will automatically detect the fan type installed, so user doesn't set "DC or PWM" mode additionally under BIOS setup.

Intel^® N3000 Series SoC, 100 / 200 Series and AMD AM4 chipset has removed their support for the Enhanced Host Controller Interface, so you might find it difficult to install windows7 operation system Since the USB ports won't work.
Please refer to the Web page from following to install Windows7 on AM4 platform mothebroards.
The link is below:
http://www.asrock.com/microsite/Win7Install/index.html