Windows 10 Reinstalled windows 10. Ext HDD isn't working now.

Good idea Pat. Of course if that external drive has failed, the data being copied over may be corrupted since it's being copied from a failed HDD source. If this doesn't work, you should consider testing the drive using the instructions here: Link Removed
USB drives from Toshiba can be difficult to test, as Toshiba doesn't make their own drives and haven't for 2 decades. They use Fujitsu or Samsung. If none of the links work to test the drive, you can take it into a local repair shop and pay them to test it for. Alternatively, you can remove the drive from it's enclosure and insert it into a Drive Caddy device and test on a desktop PC; the Caddy is less than $20 US available here: Link Removed

Of course, if the Toshiba drive fails and HDD diagnostics test in the desktop PC setup with the Caddy that drive has failed and it must be replaced! Since you mentioned the Toshiba external still reads ok on a non-W10 computer, you can copy everything off from it to the internal HDD on the desktop and then over to one of your other working-in-W10 externals you mention. Or if you plug in one of the other working externals to the desktop PC and the Toshiba via the Drive Caddy; you can do a volume-to-volume copy using the W10 File Explorer. Once you get your stuff off the Toshiba, you can continue to test it. If you are unable to do so, you should then just junk it or only use it on non-W10 computers; but if it fails on W10 I would personally junk it, as it's not a problem from W10; it's a red flag indicator that the Toshiba drive is failing.

Best of luck,
<<<BIGBEARJEDI>>>