nVidia GPU working only after restarting

[Mormislaw]

Hi
I'm using a 1,1 Mac Pro on El Capitan.
I have a GTX750 alongside the original 7300GT installed with the latest driver for this version.
However, when I boot the system, there's no image. I have to reboot the Mac a few times, then it starts to work.
Can you please help me?
Thanks in advance

 

[orph]

have you tried pulling one card testing, pulling second card testing or changing display cables?

 

[Mormislaw]

Yes, it doesn't not work with the first slot (16x), however it does in second (8x) one. Now I tried changing them again, and now the GTX750 does not work at all

 

[orph]

with just one card installed that happened ?
may just be dust in the slot, its happened before