A bit of a odd one. System Motherboard - Gigabyte Z77-D3H CPU - i5 3570K Crucial_CT500MX2 SCSI Disk Device (SSD) with windows 10 & programs. (C) 2TB Western Digital WDC WD20EFRX-68AX9N0 SCSI Disk Device (SATA) for backup. (D) I unplugged the WD Hard drive and when I attempted to boot I got 'bootmgr missing'. I reconnected the WD drive but still coultn't boot the PC. I run start up repair and this couldn't fix the issue. I then restored an image which worked. I have never had this happen before. Why would disconnecting the D drive cause the PC not to boot? Thanks for any help in understanding what happened.