on board NIC’s locking whole network

we have recently purchased 100 new pc’s and after setting up 10 of these new pc’s, we noticed a drastic change in network activity.
we are experiencing the whole network locking up, internet connectivity is nowhere in sight. we have noticed that the new NIC cards that are on board does not shut off after a user had logged off, it stays active and worse it changes the speed from 10T to a 100T knocking of network traffic. we tried disabling the NIC card and installing a seperate card but does anyone have a better idea other than putting an extra card. the on board card is 3c0m 3c905ctxm.