Had a very strange one today which is a totally new one on me.
We started getting calls that "The network has disappeared" and sure enough the switch for that area wasn't responding to pings (so couldn't be managed).
Physical eyes on showed that the lights were on but no-one was home so we did a power cycle.
At this point as the switch came up it was pingable but very quickly the ping times increased until it timed out and was dead again.
So, yank client connections one at a time and eventually we pull a connection and the switch comes back and starts to respond to pings and to work again.
This is where it gets a little weird..
We tracked down that port to a Dell laptop that had BSOD'd.
Now, foolishly I didn't make a note of what the BSOD error was, but I thought that once a machined BSOD's that there was essentially no IO of any kind, so I'm unclear how it could have the impact it did?
The switch is an old(ish) Netgear so my assumption is that it got overwhelmed with packets of a type it didn't like.