Arie Prins

What type of laptop and show some photos of the defect. Perhaps then a answer is more easy. How did you swicht the laptop off with a broken knob??

Normally a monitor have an indicator light. Is that one on or off? If no light it shows that 1 there is or no power supplied via main cable 2 Main cable defective, try an other one 3 Main switch? Some monitors have on the backsite a main switch and on the front a small on/off switch. 4 all ok above well your build in powersupply ias out of order. The display is not working anymore, so you can at least try to find a little fault, example a fuse on the power supply board or so. Check by metering if supply voltage is available on psu and output voltages on psu etc. BE CAREFULL FOR LIVE HIGH VOLTAGES FROM MAINS SUPPLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Forgot perhaps an connector to plug in??

There are on one side of the mainboard 4 black capacitors and in the center of then, there is a big transistor. Type is TIP127. This one is responsible for on/off switching. Try to replace and test again. I suggest however to replace this one for an TIP137, this one can handle a little more power.

It is possible that one of the connectors inside is disconnected. You have to open both sides by unscrew all the screws. Take care that there are differend screws in some holes. Dont mix them up. On one site thereis a battery. Check this one by metering if that one if working. Also inspect the driver printed circuitboard, if the connectors are all fitted. On the other half there you will find the mainboard and the driver board too. Same story inspect for disconnected connectors.