|Read the routers manual on howto setup the router and especially the wireless options.|
Therefore, you first have to connect to the router by wire, to configure it.
In the wireless security settings or the router, you should find the currently used encryption key, if already configured.
Otherwise, you have to configure it by yourself (see the routers manual).
This encryption key must also be used on the computers wireless connection, to connect to the router wirelessly.
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