Unknown formatting quandry

I received an Excel file with part numbers and am trying to use either the indexing or vlookup function to match the part numbers to the ones in our system and pull in the new price.
The problem is that when I apply the Index or vlookup formula, I get #N/A as a result. I have tried to reformat the part numbers as a number with no decimals, as text, and as general.
I have tried to copy the numbers and paste them back with values only. I get the same result. I have checked to be sure there is no conditional formatting in effect. There is none.
If I go to the cell and completely retype the part number, the index and vlookup formula pulls in the correct price. If I try to copy the formatting for the part number I just retyped to the next
part number, I still get the #N/A result. No matter what I do, outside of physically retyping the part number in the original list, I get #N/A. Has anyone else run into this problem, and is there
a solution? Thanks.

You were correct. There were hidden spaces at the end of the part numbers. I highlighted the entire column, then used Find and Replace. In the Find box I entered a space. I left the replace box empty and replaced all. That fixed the problem. Thanks for your help! Much appreciated.