Do you have access to a second Mac? If you do you can try setting up yours in Target Disk Mode and inter-connect the two systems is your system able to access your systems drive. [https://support.apple.com/en-us/HT201462|How to use target disk mode to move files between two Mac computers]
When the display goes dark see if a flashlight shining through the Apple Logo allows you to see your desktop and the icons on it.
As far as High Sierra I'm not a fan yet! If you have a SSD drive you'll want to stick with plain Sierra until Apple fixes APFS to work better on SATA based SSD's. If you have a regular spinning drive you're OK! The problem is Apple forces APFS on you when the installer see's a SSD drive.
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Sadly if you have a SSD you'll need to scratch the drive down to do a fresh install of Sierra as you can't do an inlace upgrade as you could the other way.
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Sadly if you have a SSD you'll need to scratch the drive down to do a fresh install of Sierra as you can't do an inplace upgrade as you could the other way.
But before we go down that path lets see whats happening with your system as something is not right! Let us know what you see with the two tests I outlined. Once I get an idea what we're facing will guide us on the next direction.
Do you have access to a second Mac? If you do you can try setting up yours in Target Disk Mode and inter-connect the two systems is your system able to access your systems drive. {https://support.apple.com/en-us/HT201462|How to use target disk mode to move files between two Mac computers]
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Do you have access to a second Mac? If you do you can try setting up yours in Target Disk Mode and inter-connect the two systems is your system able to access your systems drive. [https://support.apple.com/en-us/HT201462|How to use target disk mode to move files between two Mac computers]
When the display goes dark see if a flashlight shining through the Apple Logo allows you to see your desktop and the icons on it.
As far as High Sierra I'm not a fan yet! If you have a SSD drive you'll want to stick with plain Sierra until Apple fixes APFS to work better on SATA based SSD's. If you have a regular spinning drive you're OK! The problem is Apple forces APFS on you when the installer see's a SSD drive.
Sadly if you have a SSD you'll need to scratch the drive down to do a fresh install of Sierra as you can't do an inlace upgrade as you could the other way.
But before we go down that path lets see whats happening with your system as something is not right! Let us know what you see with the two tests I outlined. Once I get an idea what we're facing will guide us on the next direction.
Do you have access to a second Mac? If you do you can try setting up yours in Target Disk Mode and inter-connect the two systems is your system able to access your systems drive. {https://support.apple.com/en-us/HT201462|How to use target disk mode to move files between two Mac computers]
When the display goes dark see if a flashlight shining through the Apple Logo allows you to see your desktop and the icons on it.
As far as High Sierra I'm not a fan yet! If you have a SSD drive you'll want to stick with plain Sierra until Apple fixes APFS to work better on SATA based SSD's. If you have a regular spinning drive you're OK! The problem is Apple forces APFS on you when the installer see's a SSD drive.
Sadly if you have a SSD you'll need to scratch the drive down to do a fresh install of Sierra as you can't do an inlace upgrade as you could the other way.
But before we go down that path lets see whats happening with your system as something is not right! Let us know what you see with the two tests I outlined. Once I get an idea what we're facing will guide us on the next direction.