Does the starter even click. Do all the lights come on. Before you do anything else take the battery out and have it tested. It could be the battery is not holding a charge.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)