I upgraded to Windows 10 from the original Win7 that came with my Dell PC. It's on its own partition on a 1 terabyte HDD. After the last upgrade, it died and will not boot. The auto repair screen options are no joy. However, using an external disk to boot I can access the win 10 partition (as well as the rest of the HDD) and all its docs no problems, so its not a re-format problem. Sounds like a NTLDR problem to me, how do I replace it?