Some problems with the laptop

My lappy usually remain idle for a long time but i noticed a problem quite a time back....i.e. if i close the lid of my lappy keeping it on, it becomes dead, screen blackens and no other key functions, nothing happens and i have to power off. Now yesterday it happened without the lid closing, it just happend as it was idle for half an hour. This problem is not usual but comes ocasionally

ANy solution