MSI 815 PRO Manual page 37

This jumper provides Vcc or 5V standby setting for USB Device Power.
JUSBV2
Note: If your OS supports S3 function and you are using USB
device, the JUSBV2 must be set to 1-2 and the USB
device must be inserted on USB Port 1. Otherwise, the
system will not be able to enter S3 mode.
3
1
1
3
5V Standby
1
3
5V (default)
2-33