Howdy!
Well first off, if you aren't sure what's going on with it, it would be best to seek the advice of a Luthier in your area for a look-see to find out what exactly is going on there. It could be that the neck is bowed and a simple truss rod adjustment is all that is needed, or you might have a combination of things happening that an experienced eye can find right off. To give you an idea, around these parts a typical setup (without a new bridge or nut install) runs around 40-50$$. Assessments and estimates of repairs are usually free, so you might not be out anything to haul it around to a few shops and get the scoop from someone who can lay hands to it and nail the situation down before you start tweaking on things that might make it worse.
I personally like Epiphone guitars and they are usually quite good for the money. I'm thinking that it might have been left unstrung for awhile and the neck is warped. Easily corrected in most cases by someone who knows this stuff well.
Take Care;
Doug
"what is this quintessence of dust?" - Shakespeare