VSTI problems

I have a big issue with cubase 8 last week, when I want to add plugin, in a project, the slot or I load it, say “no effect” … if I delete a VSTI (halion sonic or other ) I can load some VST plugin, but not others, if I delete a second VSTI, I can insert other plugin (probably heavier) and so on …
as if I lacked space in my project, so I remove enough VSTI, my plugin charge to perfection, this is not a routing problem.
I have the latest update (0.40) and I even reinstalled cubase 8, I also reset my preferences via the AppData folder … well, I tried everything, the problem is still there!
The problem is the same in my version 7.5, still installed on my PC, and which is also updated.
I never experienced this type of concerns before, and I not changed the configuration of my system lately, and the driver for my sound card is updated.
I sincerely hope you can help me find a solution, because at the moment I can practically work on my projects!
Thank you in advance,
Fabrice Taboga