Involuntary Program Default - ALL Programs have same default to op

PLease someone help me! I have Windows Vista, tried to download Photoshop
today, never accomplished that because I encountered the issue that all my
desktop icons look like excel programs although they are not, and they use
excel as the default to open up. How do I fix this? I Have already tried to
change the default setting automatically, but it didn't work. Thanks Tina