Internal SSD will not mount to perform new install...

"I was also advised that it could be a faulty SATA connector"

"If I hook up the SSD via USB to the MacBook it loads just fine"

" I am typing this right now with the original HDD running 10.10.3 and everything is working perfectly"

There have been failures of the SATA cable where this would happen. I think you proved it when you were able to manipulate the SSD via USB.

foofoodar wrote:

...I was advise to Power cycle the drive, 20 Minutes on, 30 seconds off, 20 minutes on, 30 seconds off is suppose to restore the settings in the drive to a factory default, so I will try this and then attempt to reinstall OSX, if this doesn't work I am going to RMA the drive back to Crucial...

First, do you have the latest firmware? You can check that in System Information; the "revision" should be MU05. You can get the latest firmware here. And compared to some other SSD brands, the firmware update is relatively simple.

Second, the reason behind the Power Cycle instructions is here.

Third, the issue of TRIM vs Yosemite is discussed hereand the reason why TRIM is a good idea with the M500 and other SSDs is discussed here.

Since the power cycling fix is tied to power loss, as opposed to a clean shutdown, causing a problem, you could be right about what started the issue. At the same time, I'm using an M500 too and couple of times I've had to force a shutdown but without such consequences.

The problem could be aggravated by the SSD's controller running out of room to do its wear leveling if you've got the drive pretty full. Garbage collection is a process to which TRIM contributes, as you can see in the graph in this link. The controller can get by without TRIM but its success varies considerably, depending on the brand. The trouble with activating TRIM is that, with Yosemite, if certain events occur, you could brick your system. The discussion of TRIM vs Yosemite I linked to gives instructions on how get running again but you'd need to boot from a different drive and work on the afflicted drive using Terminal commands.

foofoodar wrote:

Is there a way to set overprovisioning for the M500 and would it help?...

Yes there is and, in fact, that's what I did when I first installed my M500. I have a 960 GB M500 and when I first partitioned it, I reduced the partition size by about 20% leaving the rest unused. The key is that while the user can't use that space, the SSD controller can and does and that increased the overprovisioning built into the drive by the manufacturer. That's one advantage of getting a large drive.

"doesn't make sense because I thought Apple sold these machines with SSD's"

Right, with SSDs made to operate w/ Apple computers. Historically this has always been an issue.

I've only used SSDs from OWC. They do sell a Crucial Micron 960 GB:

http://eshop.macsales.com/item/Crucial/CT960M500S7M/

I'm sure if you talked to their tech services they could tell you what's going on.

foofoodar wrote:

How come the original HDD works flawlessly on the same SATA cable then? I am not 100% convinced this is the issue yet, I think it does have the potential to be the issue depending on how a replacement SSD responds...

Because the SSD sends much more data down the pipe than the HDD does (in the same time)

It is a relatively common issue, it is cheap to fix, why argue about it. FYI, I use the Crucial SSD's, they work fine, change your SATA cable.

I'm having the same exact problem as you, HDD working just fine internally but once I put in an SSD I can't install Yosemite on it. Tried installing OS externally on the SSD and swapped it, no dice. Can you reply and tell me what worked for you?

Please start your own thread and provide detail on your problem