DHCP IP problems

Using a DHCP server I have recently experienced problems with “staying connected”. I will get a DHCP address along with the Gateway, WINS, DNS. A few minutes later the pc can no longer ping or connect to specific pieces of equipment. Switching to static using the same address I am fine. I have attempted to add a default gateway manually because the problem seem to be with routing. This did not correct the problem. Not all computers on the DHCP are having this problem. I am running one DHCP server. My question is anyone have a suggestion and is there a command to run to scan for available DHCP servers so I can be sure there is only one at this point.