Changing write privileges to hard drive

I cannot write Excel spreadsheets to my local hard drive. I have tried to change privileges through "Get Info" and "Permissions" but when I try to change to read and write, it says I do not have permissions to make the change even though I am the administrator. The only change can be made to system permissions. I have set up another administrator user account and it works fine but not in my primary administrator file. What am I missing???