There are no such things as "stupid" questions. However if you think your question is a bit stupid, then this is the right place for you to post it. Please stick to easy to-the-point questions that you feel people can answer fast. For long and complicated questions prefer the other forums within the support section. Before you post please read how to get help
every time I left my computer more than half an hour, when I came back, it wouldn't respond. I moved my mouse and press keyboard, nothing happened, but I can press alt+ctrl+delete to restart. what seems to be the problem?
To help anyone to help you we need a lot more information from you. Could you please tell us what your computer is and what version of Mint you are running. The more information you supply the easier it is to help.