Dodgy logic board or broken connector?

Hello,

Have a bit of a strange one for y'all.

Macbook Pro, 13", mid 2010.

My harddrive running Yosemite blew up, this was the original 250GB HDD.

Now, it didn't blow up completely, my guess is some damage on the disk rendered it unable to boot the system, but files could still be accessed. Will get to that a bit later.

So, I take an external 2TB USB drive and install El Capitan, which is working.

Using Diskutility I try and see if I can reformat the broken, internal drive. The drive shows up in Diskutility, but it won't let me format, partition or do anything from the OSX application, however I can sometimes unmount the drive from command line.

The drive seem to unmount, but still won't allow me to format or repartition, even using command line.

I purchase a new drive, a 500GB Western Digital that should work with this laptop and install it but the computer does not recognise the drive at all, i.e. it is completely invisible to the system, doesn't show up when booting in to any kind of safe modes, disk managers or disk utilities. The drive is getting power as I can feel it spinning.

Thinking it might be the connector or the cable, I have tried the tricks using tape etc to tighten the SATA connector, but still the same.

Have also tried another old 320GB drive previously used in a DELL desktop. The system can see the drive and the two partitions, but same thing here. Diskutil doesn't allow me to format or partition the drive.

I have not yet replaced the SATA flex cable, but suspect this could be the culprit, but wanted to ask if there could be a problem with the board?

The DVD reader works, both USB ports work, albeit one of them is slower that the other, but the system refuses to read any SD cards in the SD slot. It actually doesn't read SD cards even if I connect a USB external card reader. The funny thing is that the reader can read the larger CF cards I put in, but just not SD's. I can however read SD cards if I connect a GoPro camera. The SD cards in question work perfectly fine if I try reading on another Macbook, so there is no issue with the cards or the card reader.

Have tried other applications such as Drive Genius but to no avail.

Any ideas?