Linksys Gateway WAG54GS Router Does Not Work Wirelessly

I am having problems with my linksys wireless G ADSL gateway WAG54GS router. I am on Windows Vista/Internet Explorer. When I set up the router to work on the internet when I first bought it (several years ago), something must have gone wrong in the installation because it works only when connected to the computer by the lead, and NOT wirelessly.

While this is fine for general internet browsing etc on the main computer, my problem now is that I cannot connect anything else to it (such as my Playstation 3) because the router does not work wirelessly and I do not have the WPA key that the PS3 asks for. Is there any way can fix this without doing a complete reset on the router?

[ALSO: the router also periodically goes wrong, e.g. loses connection for no reason at all - I often have to disable and then enable the internet connection, or turn the router off for 15 seconds then switch it on again, and then it's fine again. I live in a rural area though, so it might be because of a poor connection. Our telephone connecton isn't very good either and sometimes goes wrong.]