Why thumbnails not showing in windows 7?

This seem top be a general problem while people complain about their thumbnail preview of the file is not showing in the windows 7.. to overcome this problem of troubleshooting.. do the following.. now Go to the START option , followed by all programs option, then ACCESSORIES. Then select System Tools. Then select the Disk Clean up option that is given there. Now select the Boot drive and click OK. There, select the ORGANIZE button which is located around the menu short-cut bar. In the drop down menu, select the folder and then search the options.. Now, in the folder option dialog, click on the tab ‘view’., " de select the option ‘display files icon on’ ‘thumbnails’.. now just select that that particular file type and click on the change program option, and then select the Windows Media Player option, See the video folder now, and then you will get it back again it means now that you are able to view your thumbnail of the video, like ways you can change other one.. thank you..