Cowboy cactus sick and turning brown now

[Xbandaid]

Help! I messaged the forum before to say that my Cowboy cactus (about 180cm tall) was turning yellow on top... but now its condition has worsen - it's now turning brown on top!! I've tried to move it to more light by the window, but it doesn't seem to help.. Please help!

[Pricky]

I think you should cut with a sterilized knife the sick parts.
To prevent this infections during the vegetative period you should place it outside.