Third Party Warranty Repairs are HORRIBLE!

My laptop was under warranty.  My office IT company made arrangements for the motherboard to be replaced.  The third party repair company (Unisys) decided my hard drive should be replaced first.  They replaced the hard drive, and gave an empty box to one of our employees.  I continued to experience the Blue Screen of Death problem.  The IT company again contacted Unisys to change the motherboard, which they finally did.  Meanwhile, my original hard drive is missing and the blame game begins.  At first Unisys stated that it was on its way back to wherever Dell wants them sent and that it would be awhile before it got to the facility, since they were shipped by USPS but would be shipped back to me by overnight service.  Never heard from them again.  The IT company again contacted Unisys regarding the original hard drive.  They then stated that it was left with an employee at the office (my son), which it was not.  Now my original hard drive (which had nothing wrong with it) is missing and there is nothing I can do about it.  I AM VERY DISAPPOINTED IN THIS WAY THIS WAS HANDLED BY THE UNISYS REPS AND APPARENTLY THIS IS A COMMON OCCURRENCE.  We are a small business that has about 50 laptops in use and this is terrible customer service by Dell and Unisys.  I would appreciate a response to this complaint.