VT not starting

[sicksix]

i have a vt 98 clubsport and i have the same problem.it starts and stalls just random iv been trying to work it out iv i had codes come up 12 92 31 and 35 and my key dosent allways work when i open the car just random just like my car starting random.i think it might be the bcm as it controls the central locking my mechanic looked at it with a tec 2 and he still dosent know what it is.my alternator is good and battery is fine and terminals are tight .every thing is new plugs leads oil filter fuel filter even new bushes in the starter motor all fusses are good any help would be great...