Instable network connection after update

Due to a hard-drive broken down, I've added two new seagate barracuda drives to my XPS 8100 and upgraded to windows 8.1 64bit. In order to get my new drives in raid1, I've updated the Bios in advance.

Since then, my network connection (LAN) keeps popping off after a couple of minutes. After rebooting, the network connection is perfect for a couple of minutes again.

I downloaded the latest driver and installed it, but no result.