I lost the software years ago, but plug and play and it works.
However, occasionally it will show me online and firewalled, but the internet will not work.
I will have to disable and re enable the network or reset the router to regain connection. No warning ect just randomly.
See if there are are updated drivers for your network card in the PC and check for updated firmware for the router. I’m assuming XP has all it’s various service packs and updates.
If you never changed it the password for every linksys I’ve seen is user: admin pass: admin. The router will default to 192.168.1.1 so just toss that IP in your web browser.