Angels have the Phone Box
So, Wynona and I have discussed this at length, and have come to this conclusion:
Office2013 only ever came with a keycard, no matter where you bought it from. If not installed by your system manufacturer, then you have to go online to install it. I think it makes no difference if ASUS or any other system MFG installed it - I am pretty sure on that: Keycode only starting with O2013.
I recall installing O2013 on a system for someone. I wanted them to have a backup of the install media, so instead of installing it online, I clicked a link that said "other" for installation, or after I clicked "show keycode" in the account, I then had the option to download the ISO for installation offline.
If you can, grab the ISO, burn to disk, completely uninstall Office, reboot, clear out registry of all Office entries using Ccleaner, reboot again, and reinstall completely. That's what I would do. But first, make sure that corrupted Excel file is completely gone from the system, and backup any custom ribbons you may have created.
Sorry I can't give you step-by-steps with screenshots, but I am working from memory.
Failing that, a call to MS Office Support might be in order. It's obviously something to do with the Excel portion of the Office install itself, since Word works properly. Although I'm surprised that the online repair option didn't work - but perhaps something remained on the system that is messing things up. So, completely uninstalling/reinstalling may do the trick.
Sorry we couldn't be of more help. Please report back with your results.