Tipps pls? Sir, I have siemens sl2_141 modem, when toconnect 718 /691 occurs, Tipps pls?

The error you refer here are due to Bad Username/Password.
Please type 192.168.1.1 in your web browser, a pop-up window will show which require User Name and Password. Type both as admin (Please use only the lowercase letter). You will then be carried out to your Modem Configuration Page. In the Left Pan select first Reboot. From the right Pan select the lower button i.e. Restore Default setting. Your Modem will be rebooted. After booting the Modem (When all the lights are ON), again type 192.168.1.1 and use the process as above to acess the Modem Configuration Page. Now select the WAN from the left pan. Press the Edit button in the row for PPPoE settings. Don't change any setting shown by default and press the next button. At the end you will get a text box to type your User Name and Password. Use your Broadband User Name and Password here (Not the Portal ID & Password). click next and then save. Now again just reboot your Modem by using the upper button in the Reboot page. You can use your broadband now.
Note: If you are unable to open the Modem Acess Page by typing 192.168.1.1, ask the BSNL person to change your Modem.
Hope this will solve your problem.
For any clarification, do contact me.