Welcome to the forum Matt,
First a couple of system settings to check.
Make sure "Show thumbnails instead of icons" under Start, R-Click (My) Computer, Properties, Advanced System settings, Advanced Tab, Performance, Settings Button, Visual Effects Tab is ticked and that "Always show icons, never thumbnails" under Windows Explorer (any open folder), Tools (in the "Menu Bar"), Folder Options, View Tab is unticked.
Also. Delete your Thumbs cache files with the Disk Cleanup Utility (Press Start, (My) Computer, Right click C: Drive (your Main or System Drive), Properties, Click on the Disk Clean Up button)...