Thanks a lot for your help. I really want Mandriva to give a try.
The laptop is new (only 6 months); of course it still could be a faulty drive, but I manage to solve it in Ubuntu, following the instructions that I found here
so I think it is more likely to be a linux problem (windows has a gently shutdown as well)
I tried to apply the same solution in Mandriva, but they did not work.
The instructions in the above link are as follows:
write a file at "/etc/rc0.d/S00hdd-shutdown-workaround" which includes this two lines:
echo 1 > /sys/class/scsi_disk/0\:0\:0\:0/stop_on_shutdown
then make it executable ("chmod +x filename")