Unless you have turned wizards off, the wizard will pop up to help you when you add a combobox to a form. The form wizard isn't smart enough to create the combo initially. Once you understand how they work, you can right-click on a text box and ask Access to convert to a combo but you need to know what all the settings need to be. So, for now, delete the text box, add the combo in its place and follow the wizard. You need to do two things after the wizard is done:
1. change the name of the combo to something meaningful like "cboMyFieldName"
2. Change the tab order on the form so that the combo replaces the text box in the sequence as the user tabs through the controls.