either alpha or numeric it wont work mixed as it sees first number after the last letter
put letter in cell then number in next cell is all i can advise
If you always have two letters in front of the number, create a new column in your worksheet and use the formula =VALUE(RIGHT(A1,LEN(A1)-2)) and fill the formula down to the end of your data. This will give you just the number part and you can then sort on the new column. That of course assumes your numbers are in column A - you will need to adjust the formula to use the correct column letter.
Not sure if it'll still work, but I used to type in the numbers 1 - 4 in the first column (A1, A2 etc.), then highlight all four boxes and then place my cursor on the little box that would appear in the bottom right hand corner of A4, drag the cursor down column A and that would automatically put the numbers in numerical order.