Desktop freezes in 10 minutes.

Hi.

I'm using Ubuntu 18.10 + Unity + Radeon(HD6670). Then, my desktop certainly freezes in ten minutes after login.
Only mouse can move but I can't click. Also, the sound is still working. But the display freezes and not change any more.
Behavior is almost same as the following;

https://askubuntu.com/questions/783501/what-do-i-do-if-ubuntu-16-04-freezes-but-i-can-move-only-the-mouse

I have no way except Alt+PrintSc+REISUB.

I also found that if I set the desktop icon not to be showed by the following command;

$ gsettings set org.gnome.desktop.background show-desktop-icons false

desktop works (at least 4 hours, but I sometimes run across freeze after 8 or more hours even if I exec the command).

Does anyone have any idea to fix this bug? I can do additional experiment.

Best Regards.