I want to quickly resolve this complexity.

Since this is an Excel issue rather than a Dell issue, you might have better luck posting on the Microsoft forums.  But wherever you post, if you want a quick resolution, you need to provide more information.  Just saying that you can't open some xlsx file reliably doesn't really give anyone who reads your post anything to work with in terms of suggesting resolutions.  Here are some useful data points you should provide:

- What version of Excel are you running?  And what version of Windows?
- What happens when your xlsx file doesn't open reliably?  Does Excel hang, crash, display an error message, or something else?  If it shows an error, what's the error message?  Have you identified any pattern at all in the unreliability?
- Is it just one particular xlsx file or any xlsx file you try to open?  What if you open Excel directly without choosing to open a specific file?  Does that always work, or is that unreliable as well?
- What have you done thus far to try to fix it, such as running a repair installation of Microsoft Office or completely uninstalling and reinstalling it?  Have you checked to see whether you have any third-party add-ins loaded in Office?  If so, have you tried temporarily disabling them?

The more information you provide, the better others will be able to help you.

A corrupt excel spreadsheet can be repaired by using Open and Repair technique. It is a built-in repair function that opens a corrupt excel file forcefully. 
 *Open MS Excel > press Ctrl+O > locate corrupt excel spreadsheet and select it.
 *Click on the arrow shown beside Open button > select Open and Repair.
 It will take just a few seconds to be completed and selected file will be opened, if possible.

In case guide on above can't assist you, then to know how to repair xlsx file you may from Google results...

https://support.office.com/en-us/article/Repair-a-corrupted-workbook-153a45f4-6cab-44b1-93ca-801ddcd4ea53

The last two links should be viewed very skeptically - they can easily be data security risks.