Hi Bruce,
There can be a number of causes, including a possible drive hardware failure. Is it slow once you have booted up into Windows?
The slowness can be from Windows trying to find files that are corrupted.
You can try the following for Windows corrupted files:
***++From CMD Prompt++ Run the following***:
* Chkdsk /F
* ``''SFC /scannow''``
* ''Dism /Online /Cleanup-Image /RestoreHealth''
***Of course there is always running a complete anti-virus/malware scan.***
***Checking Device Manager for hardware driver problems could also help.***
# Open the “Run” dialogue box by pressing and holding the Windows key, then press the R key (“Run”).
# Type devmgmt.msc.
# Click OK .
# Check the drivers' list and expand the list if necessary.
# Look for exclamation marks by the device.
# Once you find the corrupted driver, right-click on it and select Update driver from the context menu.
Reboot computer.
Let us know how it goes.