can a low GPA(LESS THAN 3/4) get into HBS? got a 750 GMAT?

I'm sure at some point, someone got in. However, those with a poor showing in one area, have to make up for it in spades in others.

Take Dominique Foxworth (HBS'15) as a famous recent example. He got in with a GMAT of 570, which is obviously significantly lower than his peers. On the other hand, he played in the NFL for years, and served as the President of the NFL Players Association, where he represented all football players in negotiations with the League. Certainly a unique experience relative to all the other bread and butter bankers, analysts, and consultants.

There are a lot of people out there with high GMATs *and* high GPAs. In fact, your five years of work experience may even work against you. In any case, you have to have something that makes you especially unique to overcome those other factors.