Question
QUESTION: Joan,
I have a 10 year old cactus (not sure what type) that grows leaves on the top and is almost 3 ft tall.  I recently moved him (Spike,that's what we call him) into the house and the entire top part has started to die and wither.  I'm not sure what the problem is.  I think it may be too cold near the window or not enough sun.  How can I save him?  Thanks Julie

ANSWER: Hello Julie,
Have you overwatered it recently?
It might be too cold, or it isn't getting enough sunlight. It depends on the conditions. It should have full sunlight for atleast 4 hours and temperatures should be above 70 degrees (F) in the warm months and 60 degrees in the winter. Also, allow the soil to dry between waterings.

I'm not sure wether your cactus may survive. Once it has started to rot, chances are low to saving it. But give it a shot:)

---------- FOLLOW-UP ----------

QUESTION: Joan,

I usually water him once a month.  Do you know what type it could be?  I couldn't find a picture of it online.  Would you suggest cutting it down or re-pot him?  How should I cut him without making it worse.  
thanks again Julie

Answer
Hello Julie,
Deciding to cut down the dying parts depends on the structure of your cactus. If it has multiple leaves, then cutting some of those dying leaves would be okay. However, if the cactus is a single or double stalk, I don't recommend cutting it. Infact, the top parts are where the new growth develops. It may not continue to grow unless you have a fortunate cactus that may successfully heal and recover. Repotting might help, if it is in a small pot or the soil is not the correct type. Use cactus soil. Regarding the watering, only water the plant as soon as the soil dries.