Weird problem with workgroup & windows XP

I have a 15 computer network, until last friday it was working perfectly. But today if I go to "My network Places" it says that I can't access the workgroup, and says "acces denied" or something.

But if I go to the command line I can map a network drive. And also if I open an explorer window and write the local address to the terminal I want to access I can do it. And all the computers have internet access. But if I go to My network places I get Access denied.

Also tried to ping the computers and nothing. I can ping the gateway but nothing else.

 

If you go to setting on local area connection, do you have the "Client for Microsoft Networks" client installed?
Also check if File and print sharing is listed there...

 

yes, it's installed, already checked that, and until last week it was working perfect. and also if that wasn't installed I wouldn't be able to access one of the computers using the explorer or anything like I did.

anyways today is working without any trouble.