Dworkin

Sorry for the late reply; I kind of put this off for a while as I haven't had the time to deal with it. Anyway, the issue was resolved after I randomly decided to install all the optional patches in Windows Update (I never bother to install those since they're optional and I like to avoid potential bloat, but lesson learned), so I'm deducing this was a Windows 7 bug which, by a very specific set of circumstances, triggered the symptom I described. Your help was certainly appreciated though.

I have stated that the problem systematically disappears when the PC in question is disconnected, or when the laptop is online. As far as proof goes that it's network related, I don't see what more you could want. As stated in the other thread, I've already tried Event Viewer—nothing relevant there. Procmon: I did what you said, and it just triggers a crap ton of explorer.exe entries, many of which are mp4 related, but I have no idea what to do with them. Wireshark: Just clicking an MP4 indeed triggers a series of SMB/SMB2 packets from 192.168.0.91 (PC in question) to 192.168.0.94 (laptop) and back, and this doesn't happen with any other file format. If I do it while the laptop is offline, I immediately get a mix of TCP packet losses and ARP packets saying "Who has 192.168.0.94? Tell 192.168.0.91". This confirms what I already knew, but still doesn't tell me what the cause is.

Need your help with a really strange issue described here: http://www.overclock.net/t/1515736 (didn't receive any relevant help there, hence my trying here) Here's the kicker though... since then I've discovered something that isn't mentioned in that thread: the issue (which I encounter on my desktop PC) doesn't occur when my laptop is on and connected to the same LAN. Clearly, my desktop tries to connect to my laptop whenever Windows Explorer interacts with an MP4 file, but I have no idea why.