I had to fix a friends computer once, internet not working, computer running win 98 I think at the time, so after checking cables, I booted a Linux live CD, that found the internet fine.
Called tech support, told em what I had done, they said call MS so we did, told them and they said how to fix it.
I think from both tech support hotlines viewpoint I saved em a lot of time saying I had checked hardware and tried a Linux cd. Even though this was at a time when Linux was considered pure evil by Microsoft they were helpful.