Mk5 golf 2.0 tdi problem

[dhorsfall2.0GTI]

Hi all, so my sister in law has a mk5 golf 2.0 tdi, 57 plate, with bmn engine, it wouldn't start in the mornings, so changed glow plugs, was fine for a week or so, but one day when she was driving it, she says it lost all power, and cut out, now it won't start, well it does start, after trying to start it for about a minute or so, but only ticks over for about 5 secs, (it also kicks out a load of white smoke) when pressing accelerator, it does nothing, had it on diagnostics and no faults are found I'm thinking maybe an injector fault, other than that I'm at a loss, any help would be much appreciated, also it seem to flatten the battery really quickly