you might want to go a bit deeper and
go to start, run, type msconfig then open start up tab
and verify that you will let checked only scan reg, systray,
both (2) load power profile and keep your AV
apply etc...
then try again
do not forget to turn off your anti virus before scan or defrag
remember we have left them at start up.
if no result
go in DOS
and type scandisk
or give it a try out of safe mode
good luck