MY CAR WONT START :(

As you have had new plugs+battery have you tried a 3 light start?
Turn on ignition but don't start just wait till glow light has gone out then turn ignition off then repeat until the light has gone out for the 3rd time then try and start it.( you may hear boiling in the cylinders but that normal.

could be ground wire to the starter motor. first thing you should of tried was a battery swap. £48 quid for a crank sensor there £15 to buy new (there ripping you off and they know it)

the car is fitted with a ECU (computer) the car will crank but if the ecu detects a problem like a sensor does it will tell the car not to start. defiantly get the ground wires checked tho.

They probably fitted the crank sensor because that's what there diagnostic tool told them ,because tHe e.c.m. Is looking at this sensor and logging a code ,Unfortunetly there is no easy answer or magic fix ,but what you could do your self is connect a jump lead from the battery negative pole onto a good earth on the engine and see if this helps with the starting ,if so then you know that the fault is an earth lead one.Also can you hear your timer relay operating for your glow plugs,it should click.Those are basic things you can try ,But ultimately the garage has misdiagnosed the fault twice and cost yourself money therefore they should assuming they are a reputable dealer ,fix it ,after all it,s third time lucky,I would definitely return it to the garage,and speak to the manager.

Johnwillfixit - tried the 3 light start

and also, the part was £28.50 from vauxhall i bought the part myself as i didnt want to buy the £15 ones from ebay... and they charged £20 to fit the part!! its currently in the garage now (different one) and the diagnostic test showed up crank shaft sensor... so they are now trying wires etc....

bustedknuckles - i have had the heater relay tested too this was not the problem! i do need to see if teh earth wire is broken... its in the hands of different garage (third garage) which seems to be having a really good look at things... if i come to a solution i will let you guys know what the problem was.

Further to " busted knuckles " advice it might be worthwhile getting starter motor load tested .