Are you able to "wake" it up after sleep mode or does the monitor remain black. If it is able to wake back up then check your BIOS settings and see if maybe you can change the amount of idle time to something longer. I doubt this is the case since it doesn't occur with slackware but does with Mandrake. Also try going to www.mandrakelinux.com
and check the hardware compatiblility list. See if it is listed and if so wether it is fully supported or partially. If not supported you will have to search for the drivers online.