Hi,I connect to Internet through LAN at workplace. I expect no help from guys here.The events happen like this 1st Case (most frequent) can't connect to sites -> network diagnostic at adapter level (Yukon Ethernet) ->result:'reset network adapter' ->no us ->restart machine -> can connect 2nd Case (often)can't connect to sites -> network diagnostic at adapter level (Yukon Ethernet) ->result:'no problem with your network adapter' -> network diagnostic in IE7 (now 8) ->result:'check your proxy settings' -> proxy settings are alright -> restart machine ->can connect3rd Case (happened today)can't connect to sites -> network diagnostic at adapter level (Yukon Ethernet) ->result:'no problem with your network adapter' -> network diagnostic in IE7 (now 8) ->result:'TCP settings not compatible...delete incompatible settings' -> Delete -> 'Still some problem' -> 'Apply TCP performance improving settings (?)' -> 'TCP settings not compatible...delete incompatible settings' -> 'Apply TCP performance improving settings (?)' -> I delete dial n/w connection -> n/w working fineIn 3d case, somewhere during browser diagnostic, I also received a message HTTP 403 (forbidden).Sometimes (in first 2 cases) I have observed that Outlook works; but not the browser.When I try to connect to any site, it seems that the connection is established but suddenly it is prevented.I checked the event logs - no consistency there.Did a clean boot...it seemed to help. but how I should use it to diagnose the issue...Hope this helps you...

Hello, Based on your description, clean boot has mitigated your issue. To find the root cause of this issue, you may need to refer to the following KB article: (KB929135) How to troubleshoot a problem by performing a clean boot in Windows Vistahttp://support.microsoft.com/default.aspx?scid=kb;EN-US;929135 Besides, this issue may also be Internet Explorer add-on related, have you tried Internet Explorer (No Add-ons)? (Run iexplore.exe -extoff) Let us know the result if possible. If the problem persists, let me know the exact messages when error occurs and your system information (model of motherboard and Ethernet adapter, especially.) Cheers, Lionel