is this Virus??

My computer is a part of a windows 2000 domain. The problem i am facing is that when i try to ping some ip address, computer goes restart without any message or error.Later i noticed whenever i open command prompt restart happens. I am not sure but this may be a spyware or some virus. Please help in this regard.
Secondly what will the best way to prevent network from virus.Should i install antivirus on all computers?? or is there any way to do thru client server.
Please help in this regard.