Microsoft Excel fails to open .xlsx file after installing compatibility pack

[Sreedharna]

Windows XP, Office 2003 sp3, Compatibility Pack. We have one user who is unable to open xlsx files even though the compatibility pack is installed. She first gets an error that says the file type is not a recognized format. THEN the file opens in excel, but the characters are all "garbage". She is able to open any other 2007 file - both Word and Powerpoint are functioning as expected. Other people can open the same files that she is unable to. It's not limited to a particular file - no xlsx files open for her. She doesn't have this problem on other PC's. We haven't yet verified, but it seems likely, that anyone else working on her PC would have the same problem. If at all possible we'd like to avoid a re-maging.

[Bontu]

It looks the issue is related to some kind of setup. There are some similar threads on forums that you can simply read and figure out the issue. Try to read the information mentioned in the below threads.
Can not open file "Xlsx" with excel 2007
Troubleshooting “Can’t open .xlsx file” in Vista

[Shurod]

You can perform a simple restore. Because the characters that you had mentioned are junk characters which shows that the file is corrupted. I will recommend you to first take a backup and if possible try to run a full clean installation of Microsoft Office 2007