To test this open up Control Panel and choose Modems. Click on the Diagnostics tab. Select your modem from the list and click on the More Info button. If you see a list of information in the window with a bunch of ATI's and responses, your modem is working perfectly and you need to check your Dial-up Adapter settings . If your modem usually works fine but is just not working today, try shutting down your system for a few minutes.
Modems are like a primitive computer all in themselves.
Sometimes they need to be reset like a computer does. If this fixes the problem for a while but the problem comes back, consider replacing your modem. This confuses people who are used to setting IRQ numbers and port numbers manually. Often times when you install a new modem, it will try to use a port and IRQ that are reserved by the system's BIOS, such as COM1 or COM2. This causes a conflict or contention for system board resources which could cause your computer to lock-up or you modem to not respond.