open up /etc/default/acpi-support and make sure that the following options look like:

# Should we save and restore state using the VESA BIOS Extensions?
SAVE_VBE_STATE=false

# The file that we use to save the vbestate
VBESTATE=/var/lib/acpi-support/vbestate

# Should we attempt to warm-boot the video hardware on resume?
POST_VIDEO=false

# Save and restore video state?
 SAVE_VIDEO_PCI_STATE=true

# Should we switch the screen off with DPMS on suspend?
USE_DPMS=false



Can also try adding acpi_sleep=s3_bios acpi=noirq to kernel options in grub.