The behavior you describe seems to be consistent with having some tags among your ignored tags.
Many details about them can be found in the FAQ: What do “favorite tags” and “ignored tags” do? - I will quote some relevant parts.
By default, questions with these tags are shown faded; they are still visible but less prominent. If you select Hide questions in your ignored tags in the Tags section of
/users/preferences, they are hidden completely (this is done by a client-side script however, so you may notice odd “gaps”.)
There are several ways to add/remove ignored tags:
- In the tag’s tooltip, click on the star twice (or once, if you have favoured that tag).
- On the main page’s sidebar, click on edit next to Favorite Tags.
/users/preferences, use the respective field in the Tags section.
Note that you can use wildcards in the latter two.
When you hover over any tag you are shown a tooltip. By repeatedly clicking on the star in the upper left corner you can toggle between none/favorite/ignored. (Correspondingly to these possibilities the star toggles between grey, gold and red cross.)
In the sidebar on the right when viewing questions you should see list of favorite tags.
When you click on the word edit, you can edit your favorite tags and your ignored tags. (It seems that ignored tags are not shown until you click on edit. But I did not find some documentation or a post on the main meta where this detail is explicitly spelled out.)
And, as mentioned above, the third option is to go to your profile and there choose "Edit Profile & Settings" and then "Preferences".