If you are using an .accde/.accdr and you don't have error trapping, Access simply closes the database. If you are using an .mdb or .accdb, see if you can remember what you were doing when the closure happens. If you can identify the form, you can put error trapping code in any modules that have code and that should get you started. When I don't know what errors I might expect, I use a generic message that shows me the code as well as the description.
Private Sub somename
On Error GoTo ErrProc
'''' your code
ExitProc:
Exit Sub
ErrProc:
Select Case Err.Number
Case Else
msgbox Err.Number & "--" & Err.Description
End Select
Resume ExitProc
End Sub
Sorry about the code. I get an error when I use the code window to post it.