Recently spun up a new Windows 7 virtual machine on an ESX cluster. After installing VMware Tools and rebooting the machine , the NIC card would stay unconnected. You would tick the connected box , restart the machine and the Tick would untick.

The default port limit on a vSwitch if you don’t use VLAN’s to segment traffic is 120. So when you hit this limit the above happens. I increased the port limit on each host to double. The VSphere client says you need to reboot the host to apply this , but I just vMotioned the machines from one to another which seemed to fix the problem.