No power toshiba satellite 20\805-S401 laptop computer no power on none of the leds on. power adapoter is working fine,even fuse on the mother board is ok.

Make sure the charger voltage is the same as the computer.

You may have a bad DC connection:

Symptoms of a broken power jack
1. If you wiggle the power cord or the AC Adapter connector on the back of the laptop, the power LED and battery charge LED start to flicker.
2. Battery will not charge in the laptop.
3. Laptop runs fine off a charged battery.
4. With the AC Adapter connected the laptop appears to be dead.
No power LED or battery charge LED activity.
5. Laptop randomly powers off without any warning

If your laptop is out of warranty, then you can fix the problem by resoldering DC-IN jack on the system board. If it

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_8b8c2cd6ce148309

19volts is a nominal value. The AC Adapter will be fine from 18 volts up to 20volts because the power unit on the motherboard regulates the voltages very accurately.
You say you only have 0,5volts on the Mother Board power input. There's your fault. Between the Mother Board socket and the AC Adapter.
Replace the AC Adapter or Laptop Connection lead if you mean there is 0.5volts actually on the Mother Board but full oiutput from the Adapter.

check mother board may be cap or mosfet short or power pin demage

How about this step, try to turn off the laptop itself. Remove the cables and battery just like what you did before, then press and hold the power button for 10 seconds. Then, reinsert the cables and battery on the laptop and then turn on the computer itself. If the laptop restarts, shuts down or freezes with the AC power cables, two things that you should seriously consider. It might be the power cable itself, AC cable port or the circuitry going to the motherboard. And since you have cleaned out the fan and heat sink, you have isolated that problem. Have you plug-in another power cable on your laptop? If yes, then check if it works. Otherwise, the main issue is that the AC port is loose or the circuitry of AC adapter going to the motherboard is not not working. You can re-open the unit and check the circuitry from the AC port going to the motherboard. You may check the circuitry from AC port to the power supply if it is ok. If symptom persist, please contact your local dealer...

could be power related.. even a new one can fall victim of power..

You may have a bad battery. Many times laptops will not work if the battery is faulty. The first step would be to replace the battery with a new one.

Second Step: If the battery is working, then you may have a faulty AC power supply. It may be enough power being brought to power up the LCD light, but not the computer.

Third Step: Yoru mother board circuitry could be bad in the sense that some circuits are broken or the power conduit is not supplying the power to the rest of the circuits on the board.

If you are not a professional and able to troubleshoot in this manner after testing the batter and AC power supply, then I would suggest taking the laptop to a store for them to test the circuitry flow of the mother board.

The same thing happened to me today. I think it is the power supply connection to the mother board. I had to replace the motherboard 2 yrs ago with the same symptoms. I can reboot the computer 20 times and once the laptop will boot-up OK. But most of the time the power button will come one but the screen is blank. I'm not sure if I am going to get a new laptop or just replace the motherboard...again...

whats about the power board?
cheers

microscopic breaks can mess your system up... this need a techie