kiwis: I should add, I can not download any sftware
Then you will not be able to find a solution unless someone can unlock this for you by having it emailed to them.
Why can you not download any software? If you are employed somewhere that has these kinds of lockdowns, then they probably should be able to help you get the tool you need to unlock the file if it is important.
Excel password hacking is apparently quite easy, but does require a bit of software to do the job.
mysteriously... I found that (only once) that if you upload the XLS into Google Docs spreadsheet, it will open it regardless... We tried this once (only) with my colleague as he needed to get XLS opened in non-Office environment.
Alternatively, you could try open with OpenOffice if you have that.
Which version of Excel? Recent versions have better password protection so are much more difficult to break.
Most likely you'll need to download a brute force password finding tool. The free versions of such tools will typically only tell you the first 2 or 3 characters of the password, after that you need to buy the tool. If it is your spreadsheet, then the first 2 or 3 characters might be enough to remind you what the password is.