leaving your pc on should not cause that.
however that being said all windows oses are bug fests.
try rebooting and defragging your hdd.

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\"the great Modock speaks.................Listen!\" - Itachi
\"I sound like some kind of fanboy here,\" - Carnage
\"I had no idea what the hell to do\" -nxs
\"I already know god loves me more then you because he gave me good eyes\" -Gazz
the monkey will pay for the new title he has bestowed on me!