unresolved parts

hii, yesterday i found the “smiley plate” as a step file.
i opend it and resaved it as ipt, i have worked with it and everything was good and now when i opend the file it says that he cant find the part though i havent moved it or renamed it, how can i fix the problem?
thanks, ofir

edit: suddenly the parts are back as if thewere never gone, very weird