1. The usual. At the 1st of the month use canned air on the vents. Canned air and use are on the web so I don't write much more than this.
2. If you have not been keeping up the cleaning start now with a daily vent cleaning for a week, weekly for a month and then back to the 1st of the month. If this is the cause, it usually clears it up in a day or two.
3. If 1 and 2 don't pay off, I'd try a deep clean of the insides (you or a tech does this if you don't do your own work) along with replacement of the old heatsink compounds.
So I have a laptop (for 7-8 years I think), and it worked just fine until recently. I used to play games like ME, Sims 3 and other relatively demanding things, but now computer crashes even when I play literally any 3d game, and even Morrowind and Minecraft are crashing my pc now. 2d games are fine. After 15-20 minutes screen just goes black and pc shuts down, no error messages anywhere. When I attempt to run it right after crashing it would just shut down again after few seconds, so I have to wait a little. But hardware is just slightly warm so I don't consider overheat. Browser is slowed down too, usb flash I used to do readyboost now 'doesn't have enough required performance characteristics', I don't know why. I did reboot (obviously), malware scan (clean), even reinstalled os, disabled useless services, I try to run as little programs as possible at a time, checked and cleaned everything I could. Is there any way to fix this or my computer is just too old and nothing can be done? I don't know much about computers anyway and require some help.. And excuse my english too