On few of my project Cubase completely freeze. I had this issue with 7.5 and I waited to grab cubase 8 and reinstall my windows and cubase. But happening and now I am not able to work. In 90% of every project I start cubase freeze. 
And when I try to open the project I get this:
My PC:
i7-2600k
Radeon r270
Focusrite Scarlett 2i4
Windows 8.1
I’ve only had it Freeze up requiring a reboot once.
While this could be any number of things one thing I would consider is if your hard disk might be failing?
Run check disk and maybe try copying project folders to another drive to see if any fies refuse (as they have become corrupted)
if this happened to you also in previous versions i would be inclined to think its either one of your 3rd party plugs or an ongoing hardware issue. only way to determine is step by step troubleshooting procedure starting with a totally fresh daw. if the trouble still persists you will have to start the tedious task of finding the errant device/hardware/driver.