This sounds similar to a problem I posted a question about: Why does my screen not return to full brightness when waking a Lenovo B570 from sleep mode?
In this case there is a bug in the kernel which is causing the screen to be black when returning from suspended state (actually the brightness is just turned down to the lowest level). This is the bug report for the problem: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/872652 If this sounds like your problem (can't be sure as you haven't supplied much in the way of details) then there is a solution which worked for me in Comment #55 of the bug report which involves updating the kernel. When the next official update to the Ubuntu kernel is released the patch will be applied also.
Here you would have to add the following ppa to your system: ppa:kamalmostafa/stuck-backlight and enter:
sudo apt-get update && sudo apt-get dist-upgrade
Though please be VERY VERY careful and make sure the situation really does apply to you before making such changes as this, as updating the kernel can cause a lot of problems. This would only be effective if you are running the 11.10 version of Ubuntu.