797 - The modem could not be found.
This error occurs only in Windows 2000 and XP. The error can occur if the modem is no longer visible to the system, and may be a problem related to the modem driver, or system conflicts that cause the modem to work only some of the time.
In some cases, rebooting the machine may "solve" the problem.
In some cases, if the modem is not powered on when the system is booted this error may occur: shut-down, power on the modem & re-boot the system. However, it is a remote possibility.
In a couple of cases the modem was found to be improperly configured. Simply reset the modem by pressing the reset switch placed at the back of modem. A ball point pen has to be inserted into the hole provided at the back of modem and the switch inside has to kept pressed for almost 10 seconds for resetting. Then re-configure the modem to BSNL connection.
In few of the cases, the modem was found to be defective. In few cases it was found that the port in the exchange was bad.