Kirby Alarm can certainly shutdown you computer, but the problem is detecting the inactivity.
I'm sorry, but at the moment it cannot detect inactivity..
The only suggeston I have is to get KA to shutdown the computer each night at a pre set time (eg 11pm).
On another topic. I am in the process of releasing a new version of KA.
The new version is mainly to overcome problems with the shutdown, retstart, logoff functions with KA on windows 7.
It also includes a new option to update the program a lot easier the way a lot of the more modern programs do.
If you are interested you can download it from http://www.kirbyfooty.com/kirby_alarm_pro_update_v4.47.zip
To install it..
(1) Exit Kirby Alarm
(2) MAKE A BACKUP of your current kirby alarm folder
(3) Unzip the update into the SAME folder where Kirby Alarm is currently installed (making sure that you override the files)
(4) Restart kirby alarm
Let me know if you have any problems.