mini A1283 with 256 GB Sandisk X400 SSD
mac mini late 2009 model A1283
I'm upgrading this mac mini with 8 GB RAM and the 256 GB Sandisk X400 SSD. Computer runs fine and boots normally off of original hard drive which has Yosemite installed with 8 GB RAM installed.
I've been trying to get the SSD working and it now has El Capitan with latest updates. I've not been able to get this SSD drive working in the internal slot. System boots normally off the old drive in the internal slot, the system boots El Capitan from the Sandisk SSD if it is put in an external inatek enclosure. System will boot normally with the SSD in the external enclosure, with no drive in the internal slot. So long as the SSD is connected from the external enclosure, everything is fine, system runs El Capitan, and shows 8 GB RAM installed.
If I put the SSD into the internal slot, I get a grey screen. No question mark, no nothing. The only boot key sequence it seems to recognize is reset NVRAM, which I have tried multiple times. No other boot key sequences are recognized. Can't bring up boot manager, can't boot off DVD, nothing. I tried downloading an old EFI firmware update recommended elsewhere. Booted into El Capitan, it says this update is not needed.
I could just run this off the external enclosure, but would prefer to get the SSD working normally in the internal slot.