I do not know, if QCPUFreq had something to do with it, but I had this problem yesterday and fiddling with QCPUFreq and returning normal non-overclocked settings did not fix the issue.

I started by enabling lv-profile in x-terminal and then after raised the upper limit to 900 Mhz with QCPUFreq. Then noticed something was wrong, and reboots didn't fix the problem, nor reseting the settings to normal non-overclocked and non-undervoltaged levels.

Does QCPUFreq currently change the voltage levels or just change the upper limit of CPU frequency?