If there is a phone on the same line that the computer is on, make sure it is not off the hook. These may be causing interference. If you are still getting no dial-tone after checking the above things, it is possible that the modem has been damaged by a power surge. You will need to contact a hardware technician to determine if the modem has been damaged. I get disconnected randomly.
Random disconnections happen for many reasons and determining the exact reason can be difficult.
Faulty phone lines may be the cause of random disconnections. Inclement weather conditions and moisture around lines that are faulty can disrupt your connection. You can call your phone service provider and request that they check your lines. Devices like answering machines and caller ID boxes attached to the phone line may cause interference. Remove these devices and see if the connection improves.