Username/Password required on Windows XP

Sorry should have said. Windows XP SP3 HOME (fully up to date). I’ve tried the default - anonymous/‘blank’ and both user accounts on the PC - one with a password + one without - and even the router’s login/password - all to no avail. I’ve got a simple setup really. A PC connected to a router which connects to the internet and this WDTV Live box. It (the WDTV box) connects to the internet OK - youtube etc - and the ‘Check Network’ checks out OK. I just cannot get past the username/password screen when I try to gain access to the PC - BAH !!! I created a new network connection (when I thought sharing might me an issue) which allows sharing and there’s a folder (or 3) shared, but I’m so far stumped. Thanks for trying to help. I appreciate it.