I use Ubuntu 15.04 with stock kernel on my laptop. When I boot up my laptop and then try to suspend, everything works perfectly. But when I work for few hours and then try to go to suspend, it almost always freezes.
By the look of the LED, it never enters sleep mode. Just black screen. And I must forcefully shut it down.
I don't even know how to debug this problem. I looked at some log files, but didn't found anything useful to me.
Any help would be greatly appreciated.