Black screen after power on (Classic II)

Depending on the kind of sound it's making, like electrical buzzing or zapping, the powerboard could have blown out. I would recommend not turning it back on until you get a new powerboard. If that is the case.

No electrical buzzing or zapping, hdd working and cooler working but no start up sound and screen is black

The motherboard probably died. Don't know if there's any way to fix it. You would have to inspect the motherboard up close.

This guide is for the SE/30, but I'm sure most of it will still apply.

http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html#BlackOut

Some people have had success of reviving motherboards by running them through the dishwasher or cleaning the "capacitor corrosion" by hand with soapy water/rubbing alcohol. If you try this make sure you have rinsed it and let it dry completely before powering it. (Let it sit out in room temperature overnight.)

Great thanks ! I wash motherboard with soap, after in alcohol and all perfectly works, I plane to change capacitors and again wash motherboard in ultrasonic bath.

Glad to help. The Classic II is a great little machine, it was my first Mac, and I still turn it on once in a while to play around with it.

Have fun with your Classic II!

I have had good success in reviving a Classic II, and a number of other machines, just by washing the logic boards, but I leave the boards to dry for longer than overnight. I tend to give them a few days at least.

After wash i wait 5-6 hour, than clean by alcohol in the hour already it worked