There are many different BIOS types and settings used in PCs. In some cases these may be modified to suit the individual PC
environment and have no effect on the Pickering hardware. One situation we ran into was that once the 51-921 Star Fabric
PCI card was inserted into the PC, the PC would reboot when shut down or would not shut down at all.
This happened with an HP desktop PC that had an AMI BIOS but could possibly happen with other PCs and BIOS. With the AMI BIOS there is a setting under 'Power Management' listed as 'Wake on LAN'. If this is enabled the PC will reboot after shut down if the 51-921 is installed. Other BIOS may have similar settings.
In this case the information on settings was found on the HP support web site. Your PC may have this information with included documentation or be found on line.
We have seen similar behavior on industrial PCs using Intel Chip Set 945GM.