First I would contact a local Landlord Tenant Attorney who offers a free 30 to 60 minute consultation. An experienced attorney will know how to effectively handle your situation. I'm providing a disclaimer since I do not know all the specific information of your particular case. You may have a claim based on a breach of an implied warranty of habitability. I recommend contacting the landlord, and try to solve your problem.
Send a certified letter to your landlord and and keep detailed information so you can prove that your landlord ignored this information if in fact he or she does. Next, you may take him to court. I'm not sure how your local courts in Williamsport, PA handle these claims, but you may have to put the disputed amount of witheld rent in escrow. I would highly recommend contacting an experienced attorney in your area
This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.