First, please note that for security purposes, contacts bulk uploaded from a spreadsheet must be in CSV form, and can't be in excel. (To convert an excel to CSV just "Save As" then select CSV from the "Save as type" dropdown).
If you're still having trouble, try converting your data to a very basic sheet, with a row across the top containing relevant fields (first name, last name, office phone, email address, etc.), data for each contact beneath that, and little or no special formatting in the cells.
Tags / keywords: excel, CSV, upload, import, bulk, batch, multiple, format.