Secondly, if the PC were to normally drain your battery, it would have way before 6 months.
So I would go to Autozone, have them check the alternator. It is free. I would also check for loose connections on the battery terminals. That held me up for a long time.
Also just so you know a PC does drain power when "off" because it never fully gets to off (Soft Off) unless you physically detach the power (Hard Off).
What PSU do you have?
What screen do you have, and does it automatically turn on/off with the car? Does the screen have an LED that is always lit?
Do you have a keyless entry and/or remote start system? If so does it have an immobilizer bypass?
How long was the car left alone before the dead battery? Overnight, hours, or a week or two of being on vacation?