I have router in my home network. It is set to act as a DHCP server. Everything worked fine until I have added one more computer to this home network. After this, one computer always can not get IP address from router and can not access network. It is not limited to one computer but depends what computer starts up last. I hope you can provide some insight to this problem.
You say that you have configured router to act as a DHCP server. Then check IP address range that you configured. It looks like you have set router to give only two IP addresses so when third computer boots up it has no IP address. Change this setting and then everything will work fine.