Max I've held off up to this point in other posts and don't take this the wrong way but please do myself and the others here at this site a big favor and try to refrain from lecturing us on the do's and don't of tech support with CAPS throw in for added emphasis. Believe it or not before you appeared here, we made out just fine. Much to your chagrin, we have people modify their registries, extract files, change Windows settings, etc... quite often here on a daily basis and I don't recall any PCs that ended up as toast. We're quite aware of the correct way to do things. While I agree that checking the DUN settings is a good idea, my past experience is that it's doubtful that's the cause unless the DNS is somehow setup incorrectly but I've rarely if ever found that to be the case.
BTW, had you phrased it this way, it wouldn't come off as lecturing.
"Those suggestions are good ones but if I were you I suggest you check the DUN settings first before going any further ...."