The internet signal is good or bad, just look at your network cable. Or the port is broken. Test once to know if there is any problem with each port.

There are other reasons:

1, four computers have ARP attacks, push you out.

2, the bandwidth is limited, and four computers surf the Internet at the same time, which may cause your network speed to be very slow.

Your computer has its own problems. For example, there are problems with the network card and DHCP of the system.