Gigabit port speed

Hi all,

I have a 100/25 Mbps fiber optic connection with a Technicolor TG784n v3 router and I'm having problems with the speed on the Gigabit port. When I turn the computer off or restart it the speed drops to 50 Mbps. If I connect the PC to one of the other 100 Mbps ports the speed returns to the normal 100 Mbps. The company already changed the router and the problem remains the same, so I guess it's not a router problem. In fact, I found that resetting the network adapter (disabling/enabling on Network and Sharing Center) solves the problem. It's kind of annoying having to do this procedure every time I turn the computer off or restart it, so I ask for your help to find what's wrong with my PC (Windows 7 Professional SP1).

Thanks in advance.

After trying several cables and not solving the problem I ended up messing up with the advanced setttings of the network card, after reading some related stuff on the Internet. I've changed 'Link Speed & Duplex' to '1.0Gbps Full Duplex' and the problem of speed drop when powering off for a while or restarting the computer went away. But if I leave the computer off for example during one night the problem returns on the next morning. It seems the router lowers the Gigabit port speed after a long period of inactivity. Maybe some power saving feature, I don't know. Any ideas?

Thanks in advance.