halogen 12v, i never knew this and am now stuck

[Spark123]

On the output side of the trasformer, if you disconnect the lamp can you test the resistance across the leads with your multimeter set to ohms range? You should pick up the resistance of the lamp. Take the lamp out and confirm the resistance again.
If you get a relatively low reading for the first and an open circuit for the 2nd then all is well with the light and associated cabling hence I'd swop the transformer.

 

[TicklyT]

If you want to test the output you would need to load the 'transformer' to within the range usually specified on the label. That will probably be something like 12 Volts, 10 - 60 VA (or Watts). Without a suitable load, the 'transformer' could just shut down, and continue sulking until it's input is turned off, allowing it to reset.

The 'transformer' will be set up to supply an output current of between 1 and 5 Amps, but a neon screwdriver will only draw maybe a few thousanths of an amp, which is nowhere near enough for the transformer to see as a load.

Similarly, the input impedance of a multimeter set on a voltage range is probably something like 100,000 Ohms or more, instead of the range of about 5 to 10 Ohms the 'transformer' would like to see connected.

A suitable and convenient load to apply if you want to measure the output would, of course, be the lamp it will be supplying.

 

[rwalton1]

thanks for all your comments; obviously these elctronic transformers are more delicate than i had realised. Rather than the old "its either working or it isn't" there seems to be middle ground..All is working now, with new transformers.