Checking Serial Number, VBA or Function help

I have a workbook that contains the issued serial numbers for components. Column A has the serial number and Column B has the part number. I want to have a verification in column C if the serial number has been used already for the part number being entered in Column B. My best guess was to use a If/AND function to check if:

=IF(AND(B2:B100=B2,A2:A100=A2),"Used","Open")

My idea is that this will check column B if it matches B2 which is ASD01-1 and then check column A if it matches A2 which is 1. If both match the statement "Used" will be displayed. However the formula does not work. Any help on the matter would be appreciated.