If the filename extensions are HTM or HTML they will show your browser that will handle the icons associated as the icon.
It could also be that your icon cache is corrupt.
Change your screen color depth and then restore it again.
Right-click desktop in an empty area (free of icons).
Click Settings tab
Change color depth to a lower number and click apply.
Change color depth back to where it was, click apply.
Re-check disk for improper icons.