I believe the Siemens "SL2-141" is a wireless router
(not a "modem"). So I assume you are looking to retrieve/reset the password for your router. (If that's not correct, please let me know.)
There are typically two separate passwords used with a router, and it's not clear which type you're referring to. Are you trying to access the web-based
configuration page for the router (for which you need an administrator password)? Or are you trying to make a wireless connection to the Internet via the router (for which you need the wireless security key)?
You may be able to retrieve either password (or both). The administrator password would be stored in the computer that was used to configure the router. The security key should be in the computer which configured the router, as well as any computer which made a wireless connection to the router.
You may find it helpful to have the owner's manual available. (If you don't have that, you may download a copy at:http://www.iad.cz/prez/ADSL_SL2-141_User_Manual.pdf
The web-based settings for the router should be accessible at this URL (for the computer connected to the router):
The default user name is "admin", and the default password is "admin" If you can access those settings, you should be able to view the security key, or to reset the key (see pp. 99-101).
Alternatively, if the passwords are stored, you should be able to retrieve them by installing some free software.
For the computer that configured the router, download and install this program:
RouterPassView by NirSoft
For a laptop that connected to the router, download and install this program:
WirelessKeyView by NirSoft
Finally, if you are unable to retrieve the password(s) by the above methods, then you may need to reset
the router to its factory default. Note that this will delete any settings you have made (including administrator password and security key). You would then need to reinstall and reconfigure the router, starting from scratch.
If you can access the web-based settings for the router, you may then reset the router to its default by following the onscreen guidance (see p. 102 of the manual). If you can't access the web-based settings, then you can still reset the router using the physical reset button (see p. 111).. (There should be a small pinhole on the rear of the unit - simply insert a small firm object and press firmly for 10-20 seconds.)