lost sound drivers

My ME system "looses" the Soundcard driver (sigma tel
audio) which I can find using the "update driver" wizard
in Control Panel/System however although it appears to get
the driver and the sound card appears it does not work. If
I connect to the internet I can download and install a
driver and this works.
The next time I turn on the computer it has "lost" the
driver again.
System restore does not fix it (I made a restore point
after I fixed it) I have run Norton system and regestry
checks and everything seems ok
I reinstalled ME a while ago and it was all fine till last
week.
There are various other annomilies that are occuring with
my dial up networking (wrong information in the dial up
fields)
and logging on/off (does not log on to identities or let
you logg on, or says that you are in one profile but has
wrong active wallpaper and programmes)which may or may not
be connected.
Sorry this is so long winded!