when using network computer freeze

[0987123]

I using AppleTalk as network to another computer. In recent time start big problem. Whenever my colegue tried to take or copy to my computer both of them freeze an force us to restarting which is realy anoying whwn doing dealine jobs. For example: I working with Quark and when my fellow log on network to take some files from my desktop folder, all tasks immediatelly freezing.
How to fix it.