Never work right laptop

Bought two computers for my boys for Xmas. One Was fine the other worked from 12/25 to 1/15 and has never worked . Tech out TOreplace drive and motherboard. Computer doesn't work. I send it to them, they replace hard drive motherboard and any part in the computer and test it. They claim it worked. We turn it on it doesn't work now it's software so we get on phone for another two hours. Not working. Third try a tech comes and replaces parts again motherboard and hard drive. Still doesn't work. The computer doesn't turn on monitor is white no operating system. I asked for a replacement after two hours on the phone. Now they want to send another tech out. I want a replacement. Why is that impossible. I have spent more than 10 hours of my time and my money. My son needs this computer for school and he isn't be ale to use it. This is a disgrace. I have purchased numerous dell computers and did not have problems. I think dell sells  and doesn't stand by it. Now they want to fx it . I will have 8 months on my warranty they refuse to extend it. The product is terrible as is the service. An absolute disgusting display of not standing by your product I should bill dell my hourly rate for losing three days of work and hours on the phone. My service request is  Mr dell your computer sticks and I will NEVER buy from you again.  maybe I won't pay for it on my card. Kim