I have a older MacMini (1.42 Ghz PowerPC G4) I think its a 2005 model. I just bought an HP 2159m monitor. When I try to use the DVI cable included with the monitor and plug directly into the back of the MacMini the monitor doesn't work...it just puts itself to sleep after a minute or so. When I use the VGA connector plugged into the MacMini it works just fine. Why won't the DVI work? Thanks!