glow plug start diagnosis

Hola Señors and Señorita's, My ML320 CDI engine had a leaking injector for quite some time... I decided to ignorantly chug around for a while (a long while) until recently, as I thought it was getting worse. Reason I thought this was because the engine was struggling to start in a morning...

Following a minor bump to the rear of my 57 ML420 CDi it's started with some strange electrical faults. Not long after the bump, the door locks and tailgate randomly locked/unlocked whilst driving and various lights switched themselves on and off. Anyway, whilst these seem to have fixed...

Hello all, I've recently bought a Vito and am having a few problems. The glow plug light flashes for an instant, milliseconds if anything. The van won't start and i'm wondering if anyone out there knows what this might be down to? Any suggestions welcome Dan