MS Access Form where user name is selected from list

Question

I am going to rephrase a previous question that I had posted:

I have built a form in access that allows users to enter in their hours worked by activity (i.e. transactional processing, project time, vacation etc.). The fields on the form are:

1) user name 2) start date 3) end date 4) activity 5) hours spent

Is there a way to have this form in such a way that when it is opened up by a user, a prompt automatically appears that forces you to select the user name from a list of users? Than once the user name is selected, all records entered through this form have the user name field already populated (unless the form is closed and reopened again)?

Based on the user name selection in the prompt, the toggling of records using the "Previous Record" and "Next Record" arrows should strictly pertain to the selected user name selected.

** this is my current form**

steps used to produce the solution mentioned below

1) delete the combo box called "User Name"
2) add an unbound hidden text box and call it txUN
3) add the VBA code loaded below but changed the txtusername reference to user_full_name as this is the name of the column in the table that should store these records
4) created the form below with a combo box for user names and called it cbousername
5) change the frm_sample reference to [Specialist - Timesheet Entry]

Answer 1

OPTION, Open User Name form first:

Create a form like the below with a hidden textbox named txtUN.:

With the following code behind:

Private Sub Form_Current()
  If VBA.Strings.Len(txtUN & "") = 0 Then DoCmd.OpenForm "frm_UserName", acNormal, , , , acDialog
  If VBA.Strings.Len(txtUsername & "") = 0 Then txtUsername = txtUN
End Sub 

Then create a form like below. Name the drop down cboUserName.

With the following code behind:

Private Sub cboUserName_AfterUpdate()
   Forms!frm_Sample.txtUN = cboUserName
End Sub
Private Sub Form_Unload(Cancel As Integer)
  If (VBA.Strings.Len(cboUserName & "") = 0) Then
     MsgBox "You must supply a user name before proceeding.", , "ERROR: Missing Info."
     Cancel = True
  End If
End Sub

When you open frm_Sample it will check to see if txtUN has a value. If not it will open frm_UserName as a dialog. The user must select a user name and close the form. When navigating to another record if txtUsername is empty then it is assigned whatever txtUN contains.