Thanks for your answer. My first attempt will be to "repair" the SSD using the recovery Usb stick. I used EaseUS to clone Win10 from my old HDD to my new SSD. All files got copied, but the Bios refuses to boot from the SSD. I changed the boot order in bios, I even swapped the Sata cables inside the machine, so the new Ssd is in position 0,and the old Hdd in position 1. The partition is active. The bios still refuses to boot from the Ssd., although it recognises it.
I think the SSD is missing the boot sectors, while everything else is in place. I presume the repair stick can fix it. If it doesn't work, then I'll try the approach you suggested.