Haven't had that problem before, but found a couple of command line switches you can try from this article: http://www.almico.com/sfarticle.php?id=3
The /NOSMARTSCAN switch
SpeedFan uses standard calls to the OS
to access S.M.A.R.T. info.
Unfortunately, some drivers do not
work fine and cause the whole system
to crash when queried the standard
way. Such drivers included some from
Silicon Image and some others from
nVidia (for nForce 4). You will see
that every S.M.A.R.T. enabled tool
will crash with such drivers. This
switch will prevent SpeedFan from
accessing S.M.A.R.T.. You will not see
any info about your IDE or SATA hard
disks.
The /NOSUPERIO switch
The SuperIO chip contains several
functionalities. From the keyboard
interface, to floppy, serial and
parallel ports, power management and
so on. Some SuperIO chips also contain
hardware monitoring capabilities
and/or fan control support. This is
the reason why SpeedFan tries to
automatically identify them. This
works most of the time, but it looks
like that some manufacturers are using
custom devices and configurations that
collide with this detection process.
Such manufacturers include DELL (but
not all DELL products). If SpeedFan
hangs or causes your system to crash,
this switch will be a good candidate
for a fix.