windows 7 and xp wireless network - can't log into other computer.

I'm not sure what happened but I lost connections between my 3 computers on my home wireless network.  I am using a verizon fios router w/wifi.  All computers have access to wifi.  I have a Dell studio 15 laptop on wifi running Win7 that can see the other two computers on my wifi network but when prompted to log on with user name and password, to either computer, am told I have name or password incorrect.  I have a Dell XPS desktop running WIn7 hardwired to the network who can see both computers but cannot connect for same reason.  I have an older Dell dimension 4700 desktop running Xp with a wireless adapter that doesn't show the two other computers when I look under "network".  My big problem is that I have used my laptop for itunes with the Xp computer as the remote storage of all my music files and now I don;t have access to them anymore.  I tried to turn off both windows firewall and norton firewall of the XP to gain access but that didn't work.  Anyone have any ideas?  Thanks, Kevin