Dell Computer falsehoods about in-house warranty

I had purchased an in-house warranty type for a three year period on my 2006 DellDimension 5150/E510. The warranty Type is listed as NBD (next busness day). I had two calls into Dell and the gentleman tried to conince me that I should start pulling parts out of the computer so that they would know what needed repairing or replacing. I explained to him that I felt that I did not have the expertise to do this, despite being a retired physician. He argued with me over and over and would not agree to send a technician out. I ended out paying a private company each time over $150.00, the last for a new power source.