2 questions regarding memory stick and excel file?

1.I put memory stick in pc and work on some files. Now, when I want to save some typing I did on a file in a folder on the memory stick and go to save, pc box says" Cannot open the ..... 3 reasons. One reason is a file with that name is already open." I have to close file without saving revision.

2. I exit computer and then later turn on and click on drive with memory stick plugged in and it cannot access the files I previously saw when I double clicked on K-file. Blank screen where previously the screen showed the files I was typing in.