Excel 2010 :: Use Macro To Compare Two Sheets

I'm working to compare to sheet every days and i have been doing this for 2 years

I need to write macro to compare 2 columns from two sheets (sheet1 and sheet2) on same excel book and display the result on the sheet2. The number of rows and columns may not be equal and it can vary each time.

The result should be written in the sheet2 at column 'NOTES'

If serial number is blank, the result written at NOTES column =*NOT TRACK

If serial number found on sheet 1-serialNumber column, the result written at NOTES column =*Registered

If no serial number found on sheet 1-serialNumber column, the result written at NOTES column =*New registration

Example Sheet1:
PurchaseOrderNo
Manufacturer
ProductNumber
SerialNumber

PO123
Table
453154-B21

[Code] .....

I'm using excel 2010 and window 7.