My Playstation Won't Log Me on to the Playstation Network?

i have the first ps3 and yesterday it wouldn't let me log on so i left it for a day and it still won't it says it can't obtain my ip address so i moved it downstairs near the box it still won't work (its on wireless) my bro's xbox 360 works both laptops work and i checked on the ps3 website to see if it was an all round thing but it says nothing, it was a preowned ps3 when i bought it but i can't think of what to do with it HELP thank you x

Suggestion:

This either means you have typed in the 'Default Router' setting wrong or you have changed the security type on either the PS3 or your router.
You could try checking out the settings on the Xbox to make sure you have all the correct settings.
Usually when you get this messege it means your router isn't allowing the PS3 to connect to the internet, which is due to security, try turning off the security on your router to see if it makes a difference.