Siemens SL2-141

Go thro' the manual of the router there should be a resetting method for the router, ( a small hole thro which you should use some object to press a push button) in order to reset the router to factory setting, when this is done the user name and password is reset to the original factory settings with the default username and password then you can log in and re-configure your router for your ISP services.

Answer for the reset button:
It is not a button but a small hole next to the actual power button.
Get a paperclip and insert it into the hole (about 2mm width). This should reset your modem.

AT the bottom side of the modem there are many bosex. all are square except one which is round. that is your reset buttun