Macbook Pro 2010 Recognises internal Toshiba HD, then it disappears.

As you can see above - the name "diskimage" is actually the external usb drive that I have used as a boot drive when my original Toshiba HDD shipped with the MBP crashed. I have installed a new Toshiba 500 GB drive, which the MBP did not recognise immediately but did an hour or so later. I received a message to say that the HDD was not recognised, an option came up with "initialise" which I instigated. I then formatted the 500 GB drive after verification and partitioned it. When that was completed I re-booted, using the Option key in order to transfer data via Time Machine from my external back-up drive (a separate WD 500GB usb drive) to the new internal Toshiba hard drive. But the original internal Toshiba hard drive was not recognised, did not and has not appeared since.

Any suggestions on what to try next ?