Self PC timer which turns your computer idle when time out.

Now, I have an internet cafe. One administrator PC which sets time to the client PCs. Now, I have my administrator PC repaired to the technician and will get back sooner.

So, my question is that: Is there a software or a program that can manually time a PC without the administrator PC? I don't need alarm clocks or timers. I just wanted to make "When a time on the PC expires, it will somewhat like turn idle and cannot be used until I will set it another time".

Please help, Thank you.