What happened when you tried the first one? Did it produce any errors?
I haven't used Mandrake in a while, but when booting, does it say something about entering kernel parameters? (you might need to press ESC or possibly F2 or something). When you get a prompt, type:
<kernel name> (eg. linux) acpi=force
It seems that by default Mandrake uses LILO as the bootloader, in which case the config file is /etc/lilo.conf. To make the change permanent you need to add the line
to the section describing the kernel image, eg.
image = /2035-1542-sb16
root = /dev/hda6
label = linux
You'll then need to run /sbin/liloconfig (as root) to write it to the MBR.
Hope this helps.