I'm in big trouble. I built the Z390 with the i7 8-core 9700K and used a windows 10 boot USB to load Windows 10 on the PCIe NVME SSD I installed with it. All was running fine. I then hooked up the hard drives that Windows 7 used to run on with the intent of transfering as much data as I could from those hard drives (Outlook .pst and .ost files, download files, etc.). All of a sudden, blue screen of death. On reboot the system does not find the SSD drive. No matter what I do, I can't get to it. No worries I think. I'll just put my old motherboard back in and hook up my hard drives and stick with Windows 7 awhile so I can get some work done. No go! System does not recognize any bootable drive. I tried installing a Windows 7 repair disk into the CD drive, and it said that the version of computer repair on the disk was not compatible with my version of Windows. Did hooking my hard drives up to the Windows 10 machine change the boot sector on those drives? I have no idea what to do now, short of going out and buying a new system.