Unable to access chat

Hi,

I recently joined my org. offlate iam always using yahoo messenger, however since few days i am unable to visit any of the chat websites nor i can use yahoo messenger. When ever i try to visit anywebsite where i cant atleast chat using webmessenger, it closes the entire window. I cant even donwload yahoo messenger. Was it done by the network people or can i resolve the issue by my own as am the administrator of the machine. And if it was done by network people did they block using my mac address as am able to use the same on a different machine.

Please hellp