Forget the password for the excel sheet

I assume that its a very important file. There are a lot of utilities that allow you to retrieve the password from Microsoft Office files. One that I would recommend based on my personal experience is "Advanced Office Password Recovery" a.k.a. AOPR. I have used the program and its amazing, especially with Excel as you dont have to use Brute Force (mumbo jumbo in password retrieval world) to retrieve the password.