[ubuntu] monitor won't turn on when resuming from suspend

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http://ubuntuforums.org – Hi, I am using ubuntu 11.04 with a thinkpad x300. It used to suspend and wake up properly, but since last month, when coming up from suspend all turns on except the monitor and the only possibility I found to turn it on is to restart the computer. I tried to run ubuntu from an usb key, and it goes to sleep and wakes up correctly, so it should be a software problem Hibernation works fine. thanks (Hardware)