Can't open MS excel file 2003

I can't open MS excel 2003 file. I saved it in Document Library. I have Windows 7. My files in Document were a yellow color, now they are a orange color. When I click on the file, a popup shows up and it says that MS office is not installed on my computer. It also says that for the file type that I am trying to open (MS Excel), it recommends product: MS Home & Office. Please help. Thanks, Blessedgirl