I am sorry. I want to understand you fully so that I may give you a proper answer. The contract does not necessarilly have to be signed. It may be a piece of paper or email that states for example, "By allowing us to install the service, you hereby agree to the following..." Do you know if there is anything of the sort?
While I do not doubt what you tell me, rarely if ever will a company come to install such equipment without giving something in writing. This would be irresponsible of them in that they would not be protected in such situations. Perhaps there was some sort of service agreement that your son forgot about?
Normally, a person is not responsible for rented internet equipment (absent intentional damage). In exchange for the monthly fee, part of what you are provided is the requisite equipment to make the service functional. However, this situation is unique in that the equipment is installed outside of the house. That is why I was asking if there was a service agreement or contract where these terms may be spelled out. If it has just slipped your mind or your son's, then please consult it when it is found. In most cases, the company providing the rental equipment is responsible for its upkeep and replacement if it faulters. Again, this would change if stated differently in a contract or service agreement.
Unfortunately, as far as the damage to your son's computer, the company is most likely not responsible. You must be proactive in protecting the computer by the use of surge protectors or other methods of protection. Responsibilty for damage to your personal equipment has almost certainly been disclaimed.
Attorney
Licensed to practice Law in New York State