Anyone getting LAN connection errors with P35C-DS3R

[Scoubidouille]

Hello,
I am using a P35C-DS3R since 2007 and changed one year ago all my LAN equipments to support Gigabit speed (router, cabling).
It worked just fine until recently I got weird messages from this particular PC:
Whenever this PC is leaving sleep mode and comes back to life, I see msgs saying that the PC is connecting to the LAN at1Gb/s, then that the cable isn't plugged, then connecting...and after a few tries, it finish most of the time by a connection at 100 Mb/s speed. The rest of the LAN is running @1gbs whithout a itch.
I checked everything, updated drivers, swapped the Gigabit router directly connected to the PC by a different one, still Gigabit capable, with no luck. I finally changed the cable between Router and PC for a Category 6 (originally, it was Cat 5e) which seemed to make things working better for a few days but after a week or so, I am getting the same msg and most if not all connection are 100 Mb/s.
The hard and soft configurations didn't change (apart the router swap, cable and updated drivers). It looks like the board is unable to connect and stay at Gigabit speed.
Any ideas what could I do more to fix it ?
TIA!

[bluetooth]

Looks like the LAN port might be malfunctioning. Do you have another GbE port that you can use?

[Scoubidouille]

Thanks for your answer!
Well, I have a Gbe NIC on a shelf somewhere. I'll try to set it up this afternoon and test my LAN connection with it.
What's weird is that I get no transmission errors when it is connected at 100 Mb/s. I thought the NIC would be working or failing, not being between these two states....