sounds like something got hot .... reboot and examine dmp files and Event Viewer messages.
he said that the cpu fan is stopped.. its risky for him to reboot..
i suggest you to take out the heatsink and check for any damages to the processor.. like pins bent coz even if one pin is bent, it wont display.. but i feel that your heatsink might have failed.. changing your heatsink will do the job..
if you are not good at hardware.. check youtube to see videos oh how to remove and replace the heatsink etc. else, revert back here, i will help you, else,
i suggest you to take it to a service center..