[PRODIG] Viewing thumbnails - Help!

[Tim]

Just moved over to Windows 2000 and am trying out a trial of Photoshop CS but when I go to File> Open  the thumnails of Tifs and Jpgs dont dont open up into view, just the graphic.  Strangely though the thumnails of Adobe Photoshop Images show up.   The same thing happens in Windows Explorer,  I have tried all the simple things like View>Thumbnails and Customise Folder.  Is it something to do with File associations?  Anybody got any ideas how I can fix this?  Many thanks Tim