i hate to ask but I Really Need Help

I recently purchased a plinius 8200 and i am having a serious hum problem, not the kind that is bearable when the music is on, something is not right. To get to the point i am going to list all the facts that may be relevant and what i have done so far.
-i live in the south in a house that is 60 to 80 years old, i do not know anything about the wiring, i rent so any improvements to the system are out of the question.
-i switched the old two prong outlet to a three prong, i connected what appeared to be ground wires but i do not know if the are truly grounded.
-i have tried three sets of interconnects, different speaker cables, using cheater plugs, a RGPC 400, a PS ultimate oulet and different power cords in a number of different combinations to try and solve the problem which i have been sucessful in dealing with in past apartments.
-occasionally when trying different connection combos i have powered on the system and the hum is gone but if i change the volume by touching it sometimes comes back, sometimes it comes back with out being touched.
-HELP! i am completely unable to use my system at this time
i will try to promptly answer any questions that may help