The CLASSE Install Disk requires that "Legacy Boot" be Enabled and "Secure Boot" be Disabled in order for all the Install Disk functions to work properly.
Microsoft requires all Windows 8 & 10 PCs to ship with "Secure Boot" Enabled and boot method set to UEFI Only

To set up an P520, take the following steps FIRST:

To enable "Legacy Boot" and disable "Secure Boot"

1. Enter BIOS setup (by holding down or at boot time)
2. To disable "Secure Boot"
   1. Select the "Security" tab
   2. Select "Secure Boot" (3rd item from bottom of list)
   3. Set "Secure Boot" to Disabled
3. To disable OS Optimized Defaults
   1. Select the "Exit" tab
   2. Set "OS Optimized Defaults" to Disabled
4. To Enable "Legacy Boot"
   1. Select the "Startup" tab
   2. Set "UEFI/Legacy Boot" to Both
   3. Set "UEFI/Legacy Boot Priority" to Legacy First