If you translate it word by word, I mean, grammatically, "我去" mean "I will go". But we usually don't say that if we want to go, we would say "好吧!","行啊!" and the like.
On the other hand, "我去" is buzzword in internet, which means "Oh, My God!" "Holly Crap!" or the like. It is used when you feel surprised or when you are in a bad mood. The word is dialect of North China.