Q: Crossed circle on startup, impossible to install fresh OS X

I have a MacBook Pro 2009 that normally used OS X El Capitan.

I got a crossed circle on startup so I verified the disk with the Hard Disk Utility from my iMac as a target disk, as it was impossible to do it from the MacBook: everything was correct.  I copied the important files to my other computer as a backup and I proceeded to replace the OS X  with a fresh new download, as suggested in some web pages: I still got the same crossed circle at startup. As a next step, I decided to erase the disk completely and install again El Capitan, this time from a formatted USB with the OsX: no success at all, I still get the crossed circle.

I have read that the problem could be the SATA cable but if this was the case, why the disk utility no shows a problem with the hard disk? I can have access to the HD as a target, now completely erased to check it with the Hard Disk Utility of another Mac, that states that the disk is correct. How can I know if the SATA cable is the problem? I don't want to buy it unless being sure it will solve my problem...

Now I have a MacBook Pro completely useless, without an operating system installed. What should I do?

Thanks for your advise.