Hi, 

I have the same problem with my laptop (packard bell).

If you nend some file log i can send it to you. 
uname -a: 
Linux 3.13.0-53-generic #89-Ubuntu SMP Wed May 20 10:34:39 UTC 2015 x86_64
x86_64 x86_64 GNU/Linux

a part of my syslog:
[drm:rv730_stop_dpm] *ERROR* Could not force DPM to low

a part of lspci:
- VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV710/M92
[Mobility Radeon HD 4530/4570/545v]
- Audio device: Advanced Micro Devices, Inc. [AMD/ATI] RV710/730 HDMI Audio
[Radeon HD 4000 series]