KT Electronics ktelectronics.us Did not stand behind their product San Jose California

I purchased a used iMAC from KT Electronics eBAY store this summer. After receiving it, I called them because the screen was locked and I needed to get past the security screen. The man who told me he was the owner did not have an accent. He connected me with "his technical guy" who did have an obvious Asian accent. At that time they helped me over the phone. I said that I may need help later in the fall as we were remodeling our house and would not get to using the iMAC until then, and I needed to install a new OS to run a particular software, which is the reason I bought the machine. Several weeks ago I sat down to work with the computer which had sat untouched for 2 months. I unplugged a mouse via USB and plugged in a new one to the same port. From that moment on the machine went black and every subsequent time I tried to boot it up (mouse, no mouse) it got about 60% and shut down. I called back and a man with an Asian accent acted very annoyed with my problem. He said I bought it on eBay so I wasn't entitled to any help from him. I explained I had talked to a man earlier this summer who told me he was the owner, who also said I was welcome to call back for the technical help I described. I explained that I'd like to keep the machine if he could help me get it to work. He had no time for me, putting me on hold several times and saying I could not return the machine and he had no intention of helping me. I again explained that I had talked to a man who said he was the owner and he spoke without an Asian accent. I was very confused, and worried I had thrown my money away. He became very impatient and accused me of being a racist. I'm a speech pathologist, not a racist. I know accents. This response was so juvenile and combative that I sensed he knew the machine was defective. I decided to try my call again the next week and see if I could get the "real" owner on the line. Meanwhile eBay said they would request that at the very least, he send me a return label for the computer as I am rural and it is a large box. I have waited a week with no response from KT Electronics. I called again today and was met with the same combative attitude from the man who said he is KT. This has been a complete waste of hundreds of dollars and a severe disappointment. I have to wonder about the validity of all their good reviews.