I had two threads regarding to selling my hashing power and both threads disappeared, what's happening?
Well, it happens every time and there is no shame about it, it simply means, you ain't getting a few things right and as such, a review of the rules that concerns the posting technique in some section is what you need. At other times, it could be that, your post has no quality and more often, could be I the wrong board. To maintain proper forum decorum, discussions on boards are expected to be board related and in thread discussions be on point for the topic being discussed.
In the case of your both deleted threads, should you take a look at the link provided by
WelshYour most likely to come across what might be the reason behind your deleted post and how you missed your guide. Looking at the rules there, my best guess puts it at rule number
16. Do not have more than one active sales topic in the Currency exchange board. [3]
17. Trading of goods that are illegal in the seller's or buyer's country is forbidden. [2]
22. Advertising (this includes mining pools, gambling services, exchanges, shops, etc.) in others threads' is no longer allowed, including, but not limited to, in altcoin announcement threads. [8]
You do yourself some good by reading to understanding the replies and the rules of the forum at times. Always find a way to be within the forums guidelines.