post screen shot of modem page having this setting. for dial up modem it seems.
The Disconnect If Idle feature works on both the modem configuration and the connection configuration. If your modem is disconnecting after a period of idle time and you want to change the behavior, first check the connection properties. If the connection properties are not set to disconnect, then you can check the modem settings.
To check the modem settings for Disconnect If Idle, follow these steps:
1. Click Start | Control Panel | Phone and Modem Options.
2. Click the Modems tab. Select your modem in the list and click Properties.
3. Click the Advanced tab, and then click the Change Default Preferences button.
4.
On the General tab, clear the Disconnect a Call If Idle... check box, or change the value if desired. Click OK and OK again.
Some ISPs also have disconnect if the call is idle. If the settings are correct on your end, then your ISP may be disconnecting you. If this is the case, then you can have your e-mail program check for mail automatically every 5 minutes—this will keep your connection alive so that it does not time out.