Sounds like you are having an issue with your Excel software. In my experience, if that is the issue then there would be something in the Excel programming which is corrupt. The HP softwar should only interact with your computer when you are printing or scanning or using the printer's other functions. I am not sure how changing the default printer would effect non-print related tasks in a third party program.
Let me know if this information is useful to you and I will get right back with you!
-Spencer