If the fans are spinning and the trackpad is responding but there are no other signs of life, then you'll need to do some troubleshooting to figure out what's going on. Some things you can do to get more information:
• Test using charger and internal battery disconnected
• Test with external monitor with internal display disconnected
• With the battery disconnected, use an ammeter in-line with the charger to read the amperage and voltage that the system is drawing
• Test power on with other internal components disconnected (trackpad, top case, TouchBar, etc.)
This kind of testing can help you figure out which component is causing the problem. If the issues persist even when you have most components disconnected from the logic board then in most cases you can assume the issue is due to a fault on the logic board.
Good luck!