Sierra black screen issues / replaced GPU

[mecalac]

Due to my language level I'll try to describe it simply as possible.

First of all:
IMAC 27 mid 2011
16 GB RAM
256 SSD SAMSUNG + 1TB HD (factory) as FUSION
GPU replaced with geforce 765M

It worked quite fine for last years. Until sierra upgrade.
As a result: Black screen from the beginning / no possibility to boot my mac except safe mode.
In this mode I tried to install new CUDA drivers (8.0.46). It failed at 95%, but CUDA driver version has changed to the new one (CUDA widget). Then I installed new nvidia web drivers: 367.15.10.05f01. Succeed, but without any result.

I decided to switch GPU to my old Radeon HD 6770 512MB. It works perfectly now.
I opened the CUDA app, that's what I see:
CUDA Driver Version: 8.0.46 Update required
GPU Driver Version: No version found
So I managed to install CUDA again: no problem, done! Then I installed nvidia web drivers again (OK) and then restarted.

It's exactly the same in CUDA as above. Now I don't know what to do.
- I can't find any threads about problems with nvidia cards in iMacs with sierra system
- Should I switch the GPU again?
- Maybe someone knows something about replaced GPU's support.
- I guess system should boot with 765M even without CUDA drivers

Any ideas?
Beg for help!

 

[vkd]

Did you solve this problem? What was it?

 

[wiruzdk]

same problem here just installed a gtx880m i got black screen with webdriver