Agreed. I disabled and re-enabled but to no effect. The performance remains degraded. I've also tried changing the cable (shoved in a CAT5 patch) but that didn't have any effect. This is very frustrating, but there must be some solution, since clearly for a time this problem was fixed.
Do you access the server by name or by IP? I would never trust by name. Also, disable IPv6 on your desktop. Might help.
I'd try re-updating the drivers for the network card. Sounds odd but I had an issue with onboard network card once where it was fine just after drivers had been installed but then performance went downhill. In the end I solved it by installing a really old driver off the cd which came with the motherboard.
Access by IP. I manually set up the IP's of the server and the main rig for simplicities sake and so I have more knowledge about what's going on. Will try and get my hands on other drives Krazeh, and get back. edit: Working again. For now. I couldn't use the CD drivers because despite the mobo being released in September 2009 MSI didn't bother to include Windows 7 drivers, and the Vista one's (surprisingly) don't work. I got some random ones of Softpedia and installed them and am back to watching videos smoothly at 1.5MB/s, easily able to jump about the video with next to no delay in resumption of video when I skip forward or back. We shall see how long it lasts this time.