I recently got a new laptop (System76 Gazelle Professional), which came preloaded with Ubuntu 12.04. I have been using it for several days. Multiple times the screen has simply frozen, with an unresponsive mouse. Sometimes I can
Ctrl+Alt+F1 and reboot (and I recently learned I could use
sudo service lightdm restart to avoid a reboot).
I haven't been able to determine an exact cause of the freezes, but I think it sometimes happens when I minimize an open window, which makes me suspect Unity.
The problem occurred again a little while ago, and my laptop was totally unresponsive--I could not get to TTY. I was forced to hold down the power button and restart that way. When I logged back in, the system theme, desktop background, and icons on the dock had all been set back to their defaults. After several minutes, the theme and wallpaper returned to normal, but the icons are still missing.
UPDATE: I have discovered one cause for at least some of the freezes. I synced my iPod Touch with Rhythmbox, so all of the music files were transferred to the Music folder. Then, I deleted everything from the Music folder and restarted Rhythmbox. It recognizes that the files have been deleted, so they begin to disappear from Rhythmbox. After about 1/3 of the files are gone, the system freezes completely. I have tried reinstalling Rhythmbox, with no success.
UDPATE 2: Rhythmbox ran without an issue in XFCE, so I am almost positive the issue is in Unity. I still have no idea how to go about finding a solution, though.
UPDATE 3: Freezes are still occurring, in a variety of programs. Most often, the freeze happens when I do something with the mouse: open an application on the dock, close a window, press a button, etc.