DIAGNOSIS The red flashing light is a thermal overload alert. The motor got too hot and shut down to protect itself. It overheated.
FIX Unplug the power base. Let it cool down completely for at least 30 minutes. Do not try to use it. Check the extractor blade assembly. Make sure it spins freely by hand. Remove any food jamming the blades. Plug it back in. Press the cup down firmly until you hear the click.
IF THAT DIDN'T WORK The thermal fuse inside the power base may have blown permanently from a severe overload. This requires base replacement. Contact NutriBullet support.
HEADS UP This happens from running too long or blending thick, sticky foods like nut butters. Keep cycles under 60 seconds. Let it rest a full minute between cycles.