Ok - to begin I have been reading different articles on here for the last day, with little luck fixing my issue until this morning.

My laptop is currently on Windows 7 Ultimate with Office 2010, and I have zero issues opening any file on my computer. I wanted to upgrade a desktop I have from XP to Windows 7 and install 2013 Office on it. I went through the basic setup of inserting Windows 7 disk and installing the program, taking all of the downloads, and installing Norton. Next I went through the process of installing Office 2013 Pro. I then copied all the files I wanted to transfer from my laptop to my desktop on a drive and downloaded them to the desktop. When I tried to open any Excel or Word file, I got the typical "file format or extension not valid" hogwash that I've seen many complain about.

Steps I tried -
Office Virus scan to ransom virus - Clean
Repair Office - No Luck
Editing the file format on the desktop from .xlsx to .xls - No Luck
Right click on file and Open with.. - No Luck
Uploading to skydrive from my laptop - Service currently unavailable

Finally I tried copying the file on my laptop, pasting, and renaming the new one with the .xls, uploading to gmail, and finally downloading on my desktop. That solution worked out. I was able to rename it and access it. My issue is I have thousands on documents I need to transfer, and copying to rename them is not a pretty picture I'd like to see as my only answer.

Some of my excel files date back to 97 with data impossible to recreate, while even new ones created on my laptop in Office 2010 won't open. What is it with the compatibility of 2010 to 2013, or is there a common transfer error?

I can transfer a few crucial files the long way, but can anyone help with a better answer?

John