What are the laws regarding situations when a faulty piece of equipment damages another part of a system it has been hooked into?

I ask this because a USB key I recently purchased fried a few USB ports on my motherboard and I would like the company to replace the mobo.

There were no warnings or agreements in the packaging short of copyright and patent notices.

I have not contacted the company just yet because would like to know where I stand legally before I do.

Well, there may not be warranty on the device or any legal disclaimer from the manufacturer, but there are common law rules that govern this. One would be presumed assumption of risk, which is essentially the idea that if the usb manufacturer were assuming responsibility for the functionality of your very expensive motherboard after using their product, they would have charged you much more for the device itself in order to cover that eventuality. This goes back to common law cases like Hadley v. Baxendale, 9 Ex. 341, 156 Eng. Rep. 145 (1854). However, the potency of common law rules like that one are shaped and limited by how much statutes have to say about the matter in your jurisdiction. You may want to consult a lawyer about it, but I doubt the manufacturer would be held liable.

Call the USB company and complain. They will probably blow you off. Write a letter to the USB company complaining about the problem. Document this. If you don't get a response (which you probably won't), call them back. Be a pain in the ass for long enough, and they will probably replace your mobo. They are going to try to resist (because they are hoping you'll just give up), but if you build up a case by calling and sending letters and emails, then threaten legal action, they will probably relent (because they do not want to have to deal with that either!).

there is a 90% chance that the company that makes the usb key is located in china and only has a small office in the us that distributes the product. good luck getting ahold of anyone who has any authority to pay you for the mobo.

just keep sending letters and emails and if the company is located in the US file a complaint with the BBB in their home state.