why wont my central locking work on my Astra CDTI 05reg ?

Probably faulty ignition switch. The switch is at the bottom end of the ignition barrel (where you put the key to start it).
Try lubricating it (use proper lock lube, NOT oil, WD40 etc.).
If that doesn't work then you'll need a new switch, about £30 on ebay.
There is a slim chance it is the CIM module causing the problem, in which case things will start to get expensive, but I'm fairly confident putting some lubricant down the ignition switch will fix it.

spence
February 2011