不一樣，具體的不同如下

nothing serious為代詞+形容詞結(jié)構(gòu)，中文意思是不嚴(yán)重；沒(méi)什么大問(wèn)題

Just a slight cold, nothing serious.有點(diǎn)傷風(fēng)，不要緊。

not serious為副詞+形容詞結(jié)構(gòu)，中文意思是不嚴(yán)肅，不認(rèn)真

This all means that if you are serious about making more money, speak up now, on or just after May 5 - there will not be another window of opportunity for a long while.