strange dash and starting behavior

[howey]

howdy folks

my bro's b5 2000 tdi ajm, has starting acting oddly. on initial cycle of ignition the car would bleep 3 times on cranking, crank fine but fail to start. then on the 2nd attempt start fine. I thought battery as had this before with the bleeping

so fitted replacement battery only to find the car still bleeps on occasions but sometimes dose not start it seems there are 3 scenarios at the mo

1- cranks normally and bleeps, dash lights appear dim fails to start
2- on 2nd attempt dash lights as normal and car starts as normal
3- no dash lights come on at all until you turn the key to actually crank the engine, the car starts normally and only when the engine is running do the dash lights come on and go out as normal. also the climate control only then turns on with engine running opposed to lighting up as it would with dash lights

also on the odd occasion the car starts but the dash warning lights for air-bag, abs, TC remain lit but very dimly and brake warning flashes (red circle) brightly

my gut thought is ignition switch or dash unit or maybe even engine ecu?? any ideas chaps.....

many thanks

Howey