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When turning on my computer, the progress bar on the white startup screen with the apple logo in the center, gets stuck 3/4 of the way and the screen freezes. I tried option-command-p-r and was not successful. Thanks for your help!

That’s about where the GPU driver kicks in. See if it will boot in Safe Mode (hold down the Option key On start up). What OS X are you running?

I ’ ve done it. But it doesn’t work Mise à jour (13/01/2018) Wath’s the next step. Please. Thanks for helping