Well the spare lappy is about to die (been quoted up to £110 to fix it). So I am going to have to resort to the other lappy.
It is a Dell Inspiron 1510. It works fine on battery supply, but whenever I plug in any power supply the screen goes black. It is still on and processing, but I can't see diddly sqat. Any ideas, please?
Does the same thing happen when the adaptor jack is inserted - but with the mains power (to the PSU) switched off?
Most laptops have some power management circuitry that automatically dims the display when not running off the mains (to save battery power). I suspect your laptop has a fault in this circuit which results in the display switching off – rather than becoming brighter.
Check in the power settings in control panel that the power plan for on AC power isn't something strange.... try and match the plan for on battery power and see what happens then.