Ethernet card locks up

Hi
I have a problem with my router: its a PC with ROS 2.9.46 on it. It acts like a PPPoE server for around 300 users online at the same time.
The problem is that from time to time one of the ethernet cards lock up. The router continues to work so i can log in through another ethernet and simply disabling/enabling the card its start working again.
I even set up a simple script in netwatch to do this for me when the card locks up. But its still an annoying issue. Anyone have any idea what might be the problem?

The ethernet in question is: 82801EB/ER (ICH5/ICH5R) integrated LAN Controller (rev: 2)
If it’s the ethernet failing, can you recommend me some good replacement? I’m currently using rtl8139 based cards, but if there is a better solution please say.
Thanks

edit: The PC reboots from time to time (2 time in the last week). Might it be the ethernet card the cause of this reboots?