Lenovo — Lenovo laptop

Purchased laptop from Jumbo electronics Mall of Emirates Dubai and it is still understand warranty. Has trouble in booting and when I approached customer care jumbo they say that the mother board is to be replaced as its usb is broken.They are asking for more then 1000 Dirahm to be paid by me as this is mot covered I warranty.I fail to understand that how something in my laptop break as it has never fallen or miss used. I am disturbed and need an investigation by the company and early repair of my laptop free of cost as it is still under warranty. Wish to hear urgently from Lenovo thanks Gorav Rawat