The 'numbers' in the lookup column A are being stored as text, not numbers. If you enter your cursor into cell A5 after the number and then click ENTER, the number will right align and the VLOOKUP will now work. There are two options:
1. Change the text to numbers in the lookup table.
2. Change your formula to this: =VLOOKUP(TEXT($D$3,"00000"),Sheet1!$A$1:$AC$5555,2,FALSE)