Random PC randomly loses connection to the Internet

[NetworKinq]

Hello,

I have a weird situation at my office. Random PCs (they're connected to different switches and etc) loses their connection to the internet.I mean the PC that loses his connection to the Internet still can ping the gateway, but it just doesn't go through the router, seems like NAT isn't working, but at the same time all other PCs have the connection working properly.

What I've already checked:

• I can ping the gateway when internet goes down
• I can ping to the internet from another PC that is connected to the same switch and gateway
• I can ping directly from the router with LAN source
• There is no duplicate of gateway (when connection goes down the MAC address of the gateway is still the same)
• No other dhcp server in the LAN (Wireshark doesn't show that)
• Cables are good, switch restart doesn't help.

I've ran out of ideas. What else can be wrong? What else can I debug?

[marce1000]

 - How is this loss of connectivity observed ?

 M.

[NetworKinq]

It just goes down doing basic stuff - browsing in Facebook as example. It just stops to load.

[marce1000]

 - That is not specific enough as to correlate to a real network problem, the PC could have a resource problem for instance. A network problem, could be stated if all PC's loose internet access at the same time (e.g.). 

 M.

[NetworKinq]

I would say that this is pc problem but it appears on different computers, randomly. So obviously, 20 computers can not have the same resource problem?

[marce1000]

 - It depends but you will have to develop more specific networking tests , as to determine whether this is a real network problem.

 M.