Although I said I could not run chkdsk on my SSD, apparently it DOES run; it just doesn't put anything on the screen like I'm used to with an HDD. But after running cmd, entering "chkdsk /f" while the path is C:, then rebooting, the screen goes black for a minute or so, after which Windows loads. Chkdsk on a SSD, of course runs VERY fast -- so fast it probably can't put anything on screen. In any case, after doing chkdsks on both the SSD and HDD, then running Avast Quick Scan, the same message appears.