I have a windows 7 pc, it's connected to a switch through cat5 cable. Sometimes I see the the network connection icon goes into circle and I see a red X on it, but it came back after few sec. It doesn't happen very often though...so how can I tell if it's the NIC problem or the OS, software or driver problem or the switch? I have installed the latest driver and didn't help. I run continuous ping, for 4 hrs and got 3 request time out (As you can see in the screenshot)