2 OR 3 DHCP SERVER IN A LAN

RESPECTED SIR,

SIR,

In our college lan we have 2 or 3+ DHCP Server and i am having a problem... my Lab's pc are not getting ip from my DHCP server they obtaining ip from another DHCP server. 

will you please tell me the way how my Lab's PC will obtain ip from my DHCP SERVER.

THANKS YOU.