Hello Stefan, this kind of error could be caused if some Windows updates were installed recently on your system. So what you can try is restoring your computer to the last working state by choosing “System Restore” once you’re in Windows.
You can test the system out of the chassis, with minimal configuration (Motherboard, processor, power supply, 1 memory stick and video card) to narrow down the problem.
Add the working hard drive and try to boot to Windows to do the “System restore”
If the issue persisted, and if the second hard drive is still giving you that “offline member” status, even thought you replaced it, you may need to test it on another SATA port or use another SATA cable to discard if the SATA port is defective on the motherboard.
You can also try removing the CMOS battery and leave the system without it for about an hour. Then put it back on and restart the system.