After recently upgrading my Windows 7 Pro desktop (Dell Optiplex 380) to Windows 10, access to the internal D: drive (a 2T Seagate) is intermittently slow (it was working fine before). I can see and access the drive, but programs accessing files on the drive either hang up/time out or are very slow. For example, I am unable to play back audio files stored on D: without constant - and often extended - dropouts. When trying disk benchmark programs on D:, they either hang up entirely (CrystalDiskMark) or seem to work in spurts (HD Tune Pro), showing intermittent access. Any idea what could be going on?