The most likely problem is a bad phone line. This is because you have tried another modem on another computer and get the same result. This means that the problem is not with the modem or the computer, but with the phone line.
A defective modem would not work with any computer, and a defective computer would not work with any modem. A software bug could cause the modem to not respond, but it is unlikely that it would cause the same problem with two different modems. A virus could also cause the modem to not respond, but it is unlikely that it would cause the same problem with two different computers.
Therefore, the most likely problem is a bad phone line. If you are still having problems, you can try calling your internet service provider for help.