PC refuses to boot without extra non-OS drive

So today I was going to use Windows to make a system image of my OS drive in case I needed it later. However, Windows 7 doesn't allow you to choose which drives to include in the image. I currently have two drives, a 120 GB Samsung 840 EVO SSD for my OS and a 1 TB WD Black HDD for storage. After searching the forums for a while it looked like the easiest way to remove my 1 TB HDD from the system image would be to unplug its power cable temporarily; so I tried that. Upon boot, my computer asked me to either change the boot drive or plug it in and press any key. I restarted my computer and checked the BIOS boot settings, my Samsung SSD with the OS on it was indeed the stated boot drive.

I am totally baffled. Why will my PC not boot when I unplug my WD 1 TB storage drive? All I have on it are some games and programs, nothing related to the actual OS.

**EDIT**: I have been doing research, and people with the same issue as me have solved it by moving the bootloader onto the C: drive. This doesn't apply to me however because I added my WD HDD and formatted it after the OS was already installed on my SSD.

Any help is appreciated.

Specs:

Windows Seven Ultimate SP1
ASUS M5A99X EVO R2.0
AMD FX-8320 @ 4.5 GHz (1.425 volts)
Zalman CNPS9500A-LED CPU Cooler
G.Skill Ares Series 8GB (2 x 4GB) DDR3-1600 (8-8-8-24)
Samsung 840 EVO 120GB SSD
Western Digital BLACK SERIES 1TB 7500 RPM
PNY GeForce GTX 760 OC 2GB
NZXT Phantom 410 (Black/Orange) ATX Mid Tower
Corsair 600W Modular

If you post a screenshot of your Disk Management window - expanded so we can read everything - then we can usually see the problem, should it be one of the usual suspects.
Be sure both drives are connected.

Screenshots and Files - Upload and Post in Seven Forums

Nice solve!