I was running Ubuntu with an uptime for some two weeks or so.
After downloading Black Mesa Source today, I attempted to boot into Windows 7 to install the recently released mod but I got an error message before Grub2 loaded. I then booted my Ubuntu Live disc and Googled the error message.
I removed my USB sticks which eliminated that error message.
Duplicated the original Pro EVO 850 Windows 7 install onto the new EVO 840 SSD drive. Wiped the original Pro EVO 850 SSD drive (Windows 7 is now on the new 840 SSD drive). Clean install of Windows 10 onto the original Pro EVO 850 SSD drive.
On booting, I was presented with a Windows 10 screen allowing me to choose Windows 7 or Windows 10. I have been using this config for a couple of months now and both OS's are working well on the desktop.
I cant recall exactly what it was that nudged me towards the conclusion that it was my two mass storage USB sticks plugged into my PC.
I have my boot priority in my BIOS set to USB-HDD, CD Drive and then hard disk.