Hello, I am sys engg in an organisation and I am in big trouble for which I need a solution. We build pc's and some of them is got issues. When ever the user is on his Break or leaves his PC idle for 15 or 20 minutes, they can see only desktop background with no ctl+alt+del to log in to. One has to reboot the PC in order to log in. Any ideas of what could be the issue with and resolution as wellll.
Please Help me out.

Thanks in Advance.