Finding a computer in a network

Today is Holiday for me. but due to some pending works, i came office and was shocked that our development server did not work and its ip address was assigned to some other computer in the network. soon i was searching for the computer which uses the ip address of our server. i had done nmap from linux, ping from windows/linux, sent a network message thro a win messenger etc. as i was going on searching, suddenly i saw our server got its ip address and working. after that i started the web server and database server and continued working with my pending works...