A while back, I built a custom PC. Long story short, I installed a 1TB hard drive and installed Windows 10 on it. Later, I tossed a 40GB in just for the heck of it. Recently, I took it apart to replace the wireless card and update the RAM, and I removed the 40GB. It now won't boot past the CMOS. I tried jumper settings, BIOS boot/ sata port settings, to no avail. I then put the 40 in by itself, and it boots to the Wondows 10 error/ repair OS screen. With both installed, it boots fine. What the heck is going on!?