Hello Magdalena, thanks for posting here again.
1. the sentence is not full, that may be you do not understand it لم يحرك ساكنا . which means, he did nothing. A literal translation would be, he move no constant. Which an Famous Arabic idiom, and I think it is origin that he did not move any muscle, when his all muscles were fixed and not moving or may be it means that he change nothing, so every thing is constant on the position before they involvement ( to be fair, you can ask more than one person, and get different explanation from each on the origin of this idiom)
رئيس البلدية لم يحرك ساكنا في موضوع النفايات الملقاة على الأرض
2. I AM NOT SURE WHAT DOES YOU MEAN!
3.I am not sure how to answer this question, لم which is a أداة جزم which used with the present form of the present to denote it never happen in the past.
لم أقرأ هذا لالكتاب من قبل
لم أسمع هذه الأغنية
لم أرى مثل هذا العقد الجميل
لم يأتي إلى الدرس اليوم
and so on.
I hope that you are familiar with الجزم other wise it could be hard to get what I mean, and I am really sorry that I can not explain it in a better way.
you can give this video a look, it may help.
Keep learning and have a nice day.