locked out of my sheet for read only

I had closed my worksheet and when i went back to open it i
cannot update it because of message it is set to read only.
How do i remove this and how did it get that way in the first place?
I use office 2000.

You can do File | Save As to save the file with a different name, and
this new file should enable you to edit/update normally - try it first.
Then you can delete the offending file and rname the second one with
the name of the first.

Hope this helps.

Pete