Windows 7 Sharing Files with other devices.

I'm hoping that one of you geniuses can stop me from having to take drastic action and reimage my brand new pc......heres the problem. (by the way, I have read, reread and read some more on how to fix it but to no avail.)

I have a new PC running Win7 Home Premium. I also have an old laptop running XP and a media device (AZBox) downstairs. (This device is a linux based device).

Before the new PC. I could stream / transfer files to all machines, now since the new PC I cannot get files to play on the AZBox. It keeps coming up with an 'Access Denied' message and then a prompt for a user name and password.

For clarity's sake, I can see the AZBox device on the Win7 PC and transfer files to and from it. The XP machine can still see and transfer files to the AZBox. The AZBox can stream from the XP machine without any passwords.

I believe I have them all in the same workgroup (but advice on checking would be good).

I have adjusted the advanced sharing settings and they are set as follows:

Network Discovery ON
File and Printer Sharing ON
Public Folder Sharing OFF
Media Streaming ON
128 Encryption ON
Password Protection OFF
Homegroup Management ON (althugh only one Win7 PC so no homegroups used).

I have given full rights / permissions to Everyone in the individual folders.

I originally only had one Windows user account for the PC with no password. I have added a few others some Admin some Guest just to try but I'm at the point now of being completely lost.

I did try and change some security settings via Regedit to do with NTLM policies but I'm in danger of damaging something now so I throw myself on your mercy and ask for help.

Cheers
Rich