I have an identical problem, I am pretty sure it began around the time I installed the traktion waveform demo. However removing it did not fix the issue. I found that after renaming the vsttransit components startup continued until it came to any steinberg plugin such as padshop or retrologue.
If I rename all steinberg plugins I manage to start cubase but of course it is crippled. I realised at this point that I needed to rebuild windows, a task I am not looking forward to. So for now I am running cubase in a VM with no issues. btw spector and those wierd old synths seem to work ok