Hello,
First let me say, i know this problem well, it has plagues my win7 64bit machine for ages.
The quick workaround solution, is to disable and enable the network card, but i find it very anoying to add that to my boot up routine
Luckily, i found a solution:
open msconfig, go to services, remove the microsoft services from view, and close the rest. U can be selective on this, but i noticed i had an apple id xxxx service which i never asked for, and some others i could easily set on a stopped state. This solved my problem.