The system has not been shutdown properly last time.
As you overclocked the CPU as default speed, this might be the reason for that.
Therefore, for this session, the current CPU speed has been set to 500Mhz.
and should be along the lines of:
The system was not shutdown properly last time.
As you overclocked the CPU as default speed, which might have been the cause of the problem the CPU speed has been set to 500Mhz for this session,.
Athough I think it's clear enough without needing to be changed.
On a semi-unrealated issue, would it be possible to have an option to say 'No thanks, keep the CPU speed at the default' for situations where the user knows that the problem was not cue to overclocking?