what is the difference between the 3, examples welcome
As a standalone phrase (usually an answer to a request), all three are very close in their meaning: "No problem!", although the 3rd variant "не проблема" is more like "Not a problem", and is usually given when the request is an inquiry about a problem.
Ex.: "Можешь меня сегодня подбросить?" - "Без проблем"/"Нет проблем" ("Can you give me a ride today?" - "No problem") and "Можешь меня сегодня подбросить? Но мне нужно пораньше." - "Не проблема" ("Can you give me a ride today? I need it at an earlier time." - "Not a problem")
As a phrase in a sentence, all three have a similar, but distinctively different meaning.
- без проблем - there were no problems/there would be no problems (the usual context is perfective)
- нет проблем - there are no problems (the usual context is imperfective)
- не проблема - [something] is not a problem