client alway have static IP when i setup DHCP server

Hi All.

I config DHCP server have a scope is: 10.4.39.10 to 10.4.39.50
not exclude. But my PC alway obtains IP is: 10.4.39.4.

Can you help me?. When i plug new card on my PC. it obtains IP í : 10.4.39.3!!!!!!!!