MacBook Pro and SanDisk Ultra II 960 GB not working

Legacy SanDisk Products Ultra II Internal SSD
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I purchased two SanDisk Ultra II 960GB SSDs for installation into a Late 2009 27 inch iMac and a mid 2012 MacBook Pro. I absolutely could not get anything but a white screen on the 27inch. I could get the computer to boot externally via USB, but when hooked to SATA, it would not boot. OWC had some warnings about the NVidia SATA chips negotiating down to a 1.5GBs speed when trying to link to a 6G drive. I replaced it with an OWC Electra 3G drive (which worked perfectly). I returned the unopened SSD.

My next goal was to get the opened SSD into the MBP. It has Intel SATA chips and is not supposed to have any weird issues. Again, I installed the OS and booted via USB, no issues. It will not boot when installed internally via SATA. If I pop the old HD back in, it boots right away. The SSD renders a folder with a ? in the middle.

I have repartioned the drive for Mac. I also tried to clone it with just Disk Utility, same result. I suppose I could try SuperDuper or Carbon Cloner. I just installed another OWC drive in another iMac and used Disk Utility for the cloning and it worked perfectly. 

I wish I had purchased the OWC drive now, but I’m stuck with this opened drive and I would like to make it work. Has anyone else had any issues? I would think the drive is bad, but when in a drive dock, it works fine and will boot the computer via USB. 

When the SSD was in the 27 inch iMac, it would not even allow target disk mode, ot ANY boot source. I really thought the video card was faulty at first, but this drive was creating havoc.

Any words of wisdom will be welcome.

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To make a VERY long story short, the issue was the SATA cable. The computer would boot from a conventional HD so I thouhgt the SATA cable was OK.  Apparently, when these cables are failing, they can work at lower speeds, but then again may not work at all when trying to negotiate link speeds with a 6G SSD. I also noticed that with the bad cable, the negotiated link speed with the convnetional drive was 1.5 Gbps which was lower than expected. I replaced the cable from a reputable supplier and I have another SSD working. I think the SanDisk that I ended up returning was actually fine AND compatible. 

I was clued in after a brand that I know for sure was compatible would not work either. Powerbookmedic sells relaible cables. “cheap” replacements are not recommended. 

Hope this helps someone else.

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Note: the iMac 27 was a compatibility issue. Only 3G drives should be used with that late 2009 model. If you don’t beleive me, you can read about this at OWC’s website. I sintalled a 3G drive and it worked like a charm.

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This is a very typical question that you have asked over her, I am also in search of the same answer. Please let m know if this problem is being solved.