Reproduce the issue, log in, and with the system frozen collect the output of dmesg, your /var/log/Xorg.0.log, and your /var/log/kern.log.
Also, avivotool can be used to assist in debugging this issue. avivotool is provided with the radeontool package, so to install it run:
sudo apt-get install radeontool
After installing it, you run it like this:
avivotool regs all > regdump_good.txt
avivotool regs all > regdump_broke.txt
Run it two times. Once when you have a working screen, and once in the broken case (either from the tty console or logged into the sick box remotely). Attach both of those to this bug report.
Reproduce the issue, log in, and with the system frozen collect the output of dmesg, your /var/log/ Xorg.0. log, and your /var/log/kern.log.
Also, avivotool can be used to assist in debugging this issue. avivotool is provided with the radeontool package, so to install it run:
sudo apt-get install radeontool
After installing it, you run it like this:
avivotool regs all > regdump_good.txt
avivotool regs all > regdump_broke.txt
Run it two times. Once when you have a working screen, and once in the broken case (either from the tty console or logged into the sick box remotely). Attach both of those to this bug report.