Model: A1278 Year: Unknown TBD Issue: MBP boots to desktop but has slow performance. So, I loaded a new HDD with El Captain externally because the MBP wouldn't didn't recognize the new HDD internally. Now that the new HDD would boot externally via USB cable, I installed it internally to the MBP and the MBP will still not recognize it. I have already replaced the SATA cable, with no luck. Where am I going wrong? Thank you.