Same happened to me (also on Mobility Radeon 7500) on my Dell Inspiron 5100 (i was just about to file a bug report). This is what I updated last night (in case someone can figure out it has something to do with another package upgrade than xserver-xorg-video-ati but it's the only one I can come out with too. I'll attach my xorg.0.log too (where I can't find any errors explaining the problem).
Same happened to me (also on Mobility Radeon 7500) on my Dell Inspiron 5100 (i was just about to file a bug report). This is what I updated last night (in case someone can figure out it has something to do with another package upgrade than xserver- xorg-video- ati but it's the only one I can come out with too. I'll attach my xorg.0.log too (where I can't find any errors explaining the problem).