Permissions gone crazy in Excel

I can't get into my database. First it automatically set itself to read only, then when I tried to change the permissions to read & write it overrode the command and it's automatically changed itself to No access for everybody. I can't access it. It's pretty urgent as it is the cornerstone of my work! I'm using Excel for Mac 2011.
Here's what I've tried so far:

Open - it says it's read only
Close and change permissions in Get Info from Read only to Read and write
Tried to open again, permissions had automatically changed to no access and it won't open
In Sharing & permissions Everyone has No access
Tried adding a new user (myself) with different permissions but it says I'm an invalid user. Charming.
I tried the old classic of restarting the computer. No difference
I tried making a duplicate copy and it simply did nothing. Didn't duplicate.
I tried to move it to my desktop and it said “You may need to enter your username and password to make these changes” and I chose continue, expecting to have an opportunity to do so, but nothing happened.

Any kind of help would be appreciated. Thanks

Originally Posted by Domski

Mac's have OS problems!!! Surely not

Dom

Wow, thanks

I've had no issues elsewhere, and today I've been using Word, Pages and Photoshop with no problems. I'm verifying disk permissions now and will repair. It's worth a go...
Thanks for the swift reply btw

Nope, I've verified and repaired disk permissions. No cheese. Any other ideas? I think I'm dry, but this has to be solvable!