does that pot drain ??? ...

how have you been watering???

can you move the rocks and find out if the soil is wet or dry ...

whenever this happened to me.. i presumed i rotted the roots off .... you will only find out ... when you disect the pot ... [if in fact cacti have roots.. who knows.. i was guessing at the time.. lol]

ken

ps: the further question.. for the mavens... can that piece on top ... be rooted.. or propagated??? .. or whatever they do ....

I am sorry, but that plant is toast. The stock, the green bottom part, has rotted away, it is dead. The top is a form of a Gymnocalycium cactus that cannot produce chlorophyll. It needs to be grafted on another cactus. Theoretically you could regraft it, but the top looks bad too, and it is simply not worth it. Buy another one, plant it in a pot with holes in the bottom, and use half cactus soil with half perlite. But these cacti never grow really old. Try a regular cactus instead?

I find these grafted yellow or pink Gymnos are just a short-lived gimmick anyway. Rarely live long enough to flower.