DIAGNOSIS This is almost always a simple power flow problem. The blender isn't recognizing a button press because the safety lock isn't fully engaged or the battery isn't actually making a connection.
FIX First, check the physical lock. Make sure the blender vessel is twisted clockwise onto the base until you hear and feel a solid click. It needs to be perfectly aligned. If it's on correctly and still dead, try a different USB-C cable and power brick. Plug it in for a solid 30 minutes, then press and hold the power button for 3 seconds to try a hard reset.
IF THAT DIDN'T WORK The internal battery contact might be dirty or the unit could be in a deep sleep from a low battery. While it's unplugged, press and hold the power button for a full 15 seconds to force a drain. Then plug it back in with a known-good charger for an hour before trying again.
HEADS UP These rely on a specific type of USB-C power delivery. Using a cheap or old charger that doesn't support PD (Power Delivery) might show a charging light but won't actually fill the battery enough to work.