I suspect you're referring to the same issue as the poster of the previous thread, but I'm not 100% certain if I understood you correctly.
I translate a sentence and enter it (in Trados menu in Word).
What exactly do you mean by "entering the sentence in the Trados menu"? When working with Trados in Word, you have two fields: one for the source, one for the target text. Is that what you're referring to?
Trados passes to the next sentence but the source sentence stays in the document along with the translated one and main segment start and end markers.
Which is perfectly normal: you can hide hidden text and non-printable characters in Word, but this is not recommended (given the risk of damaging tags).
Finally I even can't delete the start marker.
What do you mean by this, and why would you want to delete it?