They've probably been declared [dead] because your new account has nothing except promotion of the same thing.

> my posts are not visible to anyone

You have a 21 day old account which has posted like 6 or 7 self-promotional posts in that time, and basically nothing else. What did you expect?

From the HN guidelines[1]:

Please don't use HN primarily for promotion. It's ok to post your own stuff part of the time, but the primary use of the site should be for curiosity.

> What should I do?

Contact the mods by email at hn@ycombinator.com

[1]: https://news.ycombinator.com/newsguidelines.html