I'd not give up on his just yet. They sometimes take a little time to settle into a new house.
What size tank you keeping him in, are you adding salt? What are you feeding him and how often?
What temperature is the water?
Bettas really arent bothered about the pH so long as they are kept in a constant pH they will adapt happily, they will favour a little aquarium salt to their water. Temp is a major problem with bettas, too cold and they become lethargic, their temp should be a nice steady constant 78-80 degrees fahreheit. Make sure there isnt a pwoerful current either,m if there is they tend to drape themselves onto plants and ornaments to get some respite from being blown around like a kite. Bettas have been shown to display all the sysmptoms of depression, and can become ill for what seems no apparent reason. So its essential while hes like this to ensure his water and tank conditions are pristine, and hes being fed a good nutritional varied diet. Heres a link to some foods that you could try him on to see if you can increase his interest
http://www.aquatic-hobbyist.com/fishbertspage/feeding.html
There are a couple other things that can increase a bettas interest in his surrounds, one is a common childs marble, for some unexplained reason many bettas like to push them around in the substrate. Something I havent personally witnessed but I am assured by several members of my own betta forum this is true. Something I ahave personally had a great deal of success with is a small vanity mirror outside his tank for a little while each day. This can in many instances increase confidnece and increase his willingness to defend his territory. The idea behind it is that he sees himslef and assumes its another betta, and flares at himself in the attempt to drive the interloper off. Which he will inevitably achieve as you remove the mirror. This can greatly increase his confidence and his physical stature. But it mustnt be left there for long periods of time as too much of a good thing makes mr betta a very obsessive guy, and he'll spend too much time trying to drive himself off and may actually run himself. Gotta be worth a shot. But Dont give up on him, or hes destined to return to those little cups