Putra Jaya Komputer (PJK)

I am little angry with my customer/client from Kajen which bought a secondhand printer EPSON LX-300. I work as a proffesional technician. She order to a secondhand printer. After that I am and my assistance deliver to Kajen (Pharmacy Shop). As soon as I connected a printer into LPT(Printer) port CPU. But after connected the printer just can printing one page TEST, than the printer went off. So I have got some solution, to know which make a trouble.
I am checking the printer data cable (Changing with the other one). but stiil can not printing well.
So I conclude maybe the trouble in CPU. Than I call my customer to confirm about it. She has agree if i brought her CPU and printer. And after on ours service center. I checking all everthing to find out that make can not printing well. I found which make a trouble is the WINDOWS OS has corrupted. So I had to formating and installing again but before I do it, I confirm her to ask if any important data so I can backup the data. But maybe she forget to say that on computer has insttalled important program (Pharmacy Information System/Application software). But what a pity I have to formated so the programs has gone. Actualy I can recovery that program but unfortunely she has not MASTER PROGRAM. She said to the program bought from JOGJA city. I think every Programmer must to give the master programme to there client.
After this happen, She has not yet pay which bought from me. Her husband so angry when I called her to ask pay for that printer. Her husaband bleming me on the lost of her programme. But I have argue, that is not my mistake (wrong).
Until now this problem stiil suspend.
I hope can finish it.