|Windows 7 has a 'preview' function that allows a user to hold their cursor over any running app's logo on the taskbar and it shows a preview. If you hold your cursor over the 'Show Desktop' button which resides in the bottom right corner of your screen (To the right of the date and time), it will make all windows that are up clear so you can see the desktop. When you move your cursor off of the 'Show Desktop' button, everything goes back to normal. If you click the 'Show Desktop' button, it will minimize everything and display the desktop until you bring up another program.|
Try it and let me know if that's what the issue is. If it's not, you may have bigger problems.