I didn't know that you could "link" a table to an excel sheet. Do you mean that you are importing an excel file into a new Access table? In that case, the first value of a field determines what kind of field it is. So if you have a list of values in excel:
1234
AVB
25AD
the first value is a number, so Access creates the field as a number.
There are two ways to avoid this.
1. Create a table the way you want it and then import/append the excel sheet into this table.
2. Add a row into your excel file so that you force the correct data type. For instance, in the above list, add a text entry above 1234 so Access creates this field as text not number.
HTH
Leslie