Should I withdraw my paper from a journal which even didn't give me the manuscript number after one week? I submitted an article to Elsevier which even after one week its status is still "submitted to journal" and they didn't give me even the manuscript number. I have several past experiences with this publisher, where they gave me the manuscript number promptly, but this time after one week without even manuscript number seems a little bit odd. 

Should I withdraw my article and submit it somewhere else, which probably their process may be faster? The reason why I'm asking this question is that I don't want to waste my time but on the other hand I don't want to make a bad reputation for potential future submissions by withdrawing my article because their journal is pretty famous in my field (computational physics).
One week is not an especially long time. You write that you've had previous experience with this publisher and they gave you a manuscript number promptly, but you didn't write if it's the same journal. Different journals can have different workflows - for example I've seen a journal which processed new submissions once a week, i.e. if you're unfortunate enough to submit your manuscript the day after they process new submissions, you won't get a manuscript number until one week later either.

It's up to you whether or not to withdraw, but I'll say that I've never seen an author withdraw after one week. I have however seen authors write to the journal asking about the status after one week. If you're really concerned, I would do that.