Check the outlet, clean the contacts, and try a long power button reset to revive it. If it still won't charge, the battery or internals may be shot and it's time for repair or replacement.
I used to service vacuums and the safest routine is also the easiest. Unplug it, pop out the pre motor filters, and rinse under cool to lukewarm water until clear. Skip soap since residue can cling to the fibers and cut airflow later. Press water out with your palms and blot with a towel, don't wring or twist because that can tear the foam or felt. I saw too many motors ruined by damp filters, it happens fast.
Stand the filters on edge so air can get to both sides and let them dry overnight. A fan across the room helps. Avoid heaters or hair dryers. While you wait, wipe the rubber cup gasket and check the hose and wand for clumps of fur. Reassemble carefully so everything seats fully and you should feel the suction improve right away.
