yaar until and unless u get ur pre checked from a repairs guy u wont know whats wrong. it can be as simple as loose jack or sthg as big as a blown chip/circuit. should cost between 500-1000. take it to a repairs guy and he will tell u
regarding the other problem... take it to the shop u bought it from if its new it will be in warranty, otherwise the guy can get it changed for you. there are a few repair shops in saddar audio market. try em. costs would be around 1200 to 1500 or sthg