Search:

/etc/X11/xorg.conf


Section "Screen"
Identifier "Default Screen"
DefaultDepth 24
EndSection

Section "Module"
Load "glx"

I had the same problem with a different module. Just adding it to the blacklist did nothing. I found the answer here:
http://ubuntuforums.org/showthread.php?t=1324246
From Temüjin's post:

Do...

Yes, I'm using Nvidia's proprietary drivers. Those two steps are all I did and it works fine now. It's actually better than WinXP, which sets the fans to maximum after resuming from suspend.

Any...

Thanks for that.
In case anyone else is having the same problem as me (Inspiron 5150 comes back from suspend with black screen), the solution was to blacklist intel_agp and add 'Option "NvAGP" "1"'...