I shall presume it's all on the machine not just the net connection. If the behaviour is new any updates/woods/latest hardware? Any programs still little applets for instance if you were asked to set up something for mobile network/ accessing wi-fi hot spots? You did have on trojan so. See the list of programs commencing with Windows. Still if they are legitimate programs do you require/need them to begin with windows? Try defragmenting with something else than the built-in defragmenter, for instance Smart Defrag.