Samsung Messager R450

ok i been downloading ringtones an wallpapers from myxer.com an all of a sudden after i downloaded a ringtone i couldnt open my ringtone section at all. my fone kept restaring. i took out the memory card an then it worked fine. today i downloaded 3 ringtones with out the memory card in my fone an tried to open it an then my fone restarted i out the memory card in an it did the same thing. i reset my fone an everything. wat do i do. i need help