Common cause of USB failure..... Electrical Overload.... Its common for users to use multiple devices at the same time and then use it as a charger for cell phones while supporting a USB-powered hard drive.
Worst that i have seen.... Shorted USB load or defective USB devices that overload the USB port.
Some notebook actually resets or go to power cycle to due to sudden drop in power supply voltage cause by the overload.
Its partly due to lack of education on notebook users that USB devices have limitations.
One Effective Solution:
Buy a powered USB Expansion port (Sold with Power Supply). This will protect the notebook USB devices from electrical overload.
For Replacement Motherboard:
Call Sony tech support
Go to Ebay and search for motherboard of the same notebook model as yours
There are specialty pc shops that caters for specific brands (surplus stores). In Texas are stores that sells Dell surplus parts... In CA there are stores that sell HP surplus parts.... Somewhere here in the US there has to be for Sony, Toshiba and other brands.