to be honest, don't know really wht could be causing the prob....try this out, anyway - remove the lan card, and boot up windows...now try doing a system restore to the pre-lan-card state, and install again.
go into bios and see if there's a conflict of IRQ's, i.e if the same thing happens again, boot into safe mode, go to device manager and note down the irq's of the wan miniports. now go into bios and check if some other device is having the same irq. if yes, see if you can forcibly assign a different irq for the device or the wan miniport.
btw, post wtvr hpns on the forum, plzz...i'm not sure tho