Is it possible to block members from sending pm to me?

Yes it is possible. Go up to the upper right hand corner of the page, left click on your member name. A drop down menu will appear, click on Manage Ignore Prefs. When you have done that, you will see:

Add a new user to my list, in the window below that enter the Member's name you wish to ignore, then tick the applicable boxes to the right.

When you done that, in the box marked Save Changes, click on that and you're done.

Thanks.

Will the member who is blocked know that they have been blocked by another member ?

The problem is that I still see their post names even if it the content is not displayed. Is there a way to completely remove their post names in the thread?