[xubuntu] Fuzzy login screen

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http://ubuntuforums.org – I'm experiencing a weird problem with Xubuntu recently. I had Xubuntu 12.10 installed on my desktop for some months, and sometimes, when it boots and shows the login screen, instead of displaying the default wallpaper, I get a fuzzy screen, just like an analog TV. At that time I thought I'd probably messed something up with lightdm so I didn't care. But a week ago I decided to do a fresh install of Xubuntu 12.04 on my desktop, and for my surprise, it's happening again! It's not every time, I guess around 50% of the times I turn the desktop on it happens. If I try logging out the default splash (Hardware)