Hi @andreasgaede
I realize that you removed the battery and tried starting on the power only but try a full power refresh to see if this works.
This is different because you forcibly remove all the power from the motherboard in the hope that this will reset the BIOS software in case it has become corrupted.
It seems like this has happened to your laptop as a prolonged hi-speed fan on startup generally indicates a problem with POST (power on self test). POST occurs when the laptop is first turned on and the BIOS checks that all the hardware is OK ''before'' it starts booting into the operating system (Windows) i.e. Start →POST→logo on screen→boot into Windows
The procedure is to disconnect the charger if it is connected, open the laptop and disconnect the battery from the motherboard, (you don't have to remove the battery, just disconnect it) then ''press and hold the Power button operated for a full 30 seconds'' and then release it.
Doing this drains all the power from the motherboard which resets the BIOS software back to its factory default condition as you are forcing it to try and turn on, which obviously it can't do because there is no power connected to it.
Next reconnect the battery, reassemble the laptop, reconnect the charger and check that the laptop is charging OK. If it does allow it to charge for a few minutes and then try turning in on.
''If it turns on OK'' there may be a message about the date and time being incorrect. This is normal as the BIOS has been reset. Once you correct the date and time the message won't appear the next time the laptop is started. Also any user definable settings in BIOS that you have changed to suit whatever operating requirements you wanted, will have to be changed back again as well.
''If it still doesn't work'' you may need the [https://www.alisaler.com/lenovo-y50-70-compal-la-b111p-rev1-0-schematic/|schematic] to find out what's wrong. (I think that the motherboard is an Compal LA-B111p, check what is shown on the motherboard to be sure)