If you have a Windows XP Professional and your shutdown process is very slow (you must wait minutes before shutdown command and computer is really powered off) is possible the computer cache try to empty virtual memory, and ibernation cache. This option is usually turned off by default, but third parts programs can re-enabled it.
Open, [...]

Sometimes on internet browsing is possible to meet unexpectedly adsl flipping or internet connection is momentary unavaible. When connection is back online, previously visited websites is still offline because the local cache reporting unavailbe state. In this situation is a good idea empty the local DNS cache.
Open a DOS shell (start -> run -> cmd)
write [...]