Private Sub Combo1_Click()

Res.Open "SELECT * FROM Computer WHERE ComputerName=" & Combo1.Text(I suppose you need to insert single quotes, as computername seems to be a text field), Con, adOpenDynamic

Do Until Res.EOF
Text1.Text = Text1.Text & "" & Combo1.Text & " is in " & Res("RoomName")
Res.MoveNext
Loop

Res.Close

End Sub

Anyway, debug in VB Editor and find out which line of code is causing the problem, then I think we will be able to work things out better.
Good Luck,

Rahul