Buying newer version is not an option.

I try to open excel files and it says...not a valid file format.

Searched updates and downloads for a converter or somethint to open new
versions but I cannot find anything that works...tried the SP3 for xp said
did not find expected version and quit. Cannot get compatibility 2002 to
function

Am I up the river on this or is there something...some update that will help?