when i go to change my user prefix,i see the drop down menu of some preselected stuff,but then when i try to put in my own user prefix in the box,it says that it isnt the right format or something of that such.

Same for me.
I guess there is a certain list that you can use.

Yes, only a select few will work. I have a list on my old computer which I can post here later.
It's all the normal alphabet, numbers and special figures on your keyboard and I think there are 4 or 5 special ones.

You can use any of these.
http://www.utf8-chartable.de/

Thanks trials.