Constatn disk access

I am running Vista Home Premium, 64 bit version. My computer has been very
slow for about 5-6 minutes after startup with constant disk access. I have
used the Reliability and Performance option under Administrative tools and
find that after about 2-3 minutes after startup, the only thing appearing in disk access are
numerous SVC|HOST calls with the (Local System Network Restricted) very
active. I am at a loss to debug any further. It is beyond my meager
capabilities. Can someone give me a clue as to what may be going on.

Don d