A cashier's check is not the same as a teller's check, also known as a banker's draft, which is a check provided to a customer of a bank or acquired from a bank for remittance purposes and drawn by the bank, and drawn on another bank or payable through or at a bank.
Microsoft Excel 2007, along with the other products in the Microsoft Office 2007 suite, introduced new file formats. The first of these (.xlsx) is defined in the Office Open XML (OOXML) specification.
In the case that your XLSX file doesn't open, it is highly likely that you do not have the correct software application installed on your PC to view or edit XLSX file extensions. If your PC opens the XLSX file, but it's the wrong application, you'll need to change your Windows registry file association settings. In other words, Windows is associating XLSX file extensions with the wrong software program.