You have to provide your file path along with extension. If multiple sheets are there you need to specify sheet name and session name as unique for every open excel in your process.

does excel files is closed?

Having the same issue. Even double checked the solutions above. Following and hoping for an answer...

Can you provide the error which you are getting while performing the Open Excel command?

Error is: An unknown error occurred when executing the 'OpenExcel' command. To 
continue, contact your system administrator. 
 

Also, solutions suggested by AA are: https://apeople.automationanywhere.com/s/article/Error-message-An-unknown-error-occurred-when-executing-the-OpenExceI-command 

Currently working with our IT through these but it’s definitely not solution 1,2,5,8, or 10.

Update: Cause/Solution #4 in the doc above worked. Had to uninstall and reinstall Microsoft.