Most of the threads I've found relating to this problem state that the machine powers up but the screen remains black. Not so in my case.
The problem I am experiencing is this. When testing the Suspend, everything works as expected. Computer enters sleep and I can resume from USB. But testing is usually for a short duration. When I leave the Computer in sleep for any length of time (shortest I've noticed but may be less is 1 hour) it will not wake up or power up. I do notice the LED on my case fan flash once, but other than that there is nothing. So, of course, there are no error logs.
In addition to this, the reset button does not work neither does holding the power button. I have to physically cut the power, after which I can do a normal reboot.
I'm on a clean install of Ubuntu 14.04, with a Radeon HD6790 graphics card. Thinking it may be related to the graphics card I've tried both the Catalyst v.12 and the beta v.14.
All I can think is that it must be some setting used to enter Suspend which is causing the problem.
Can anybody suggest a way to remedy the problem or something else I can try?