I agree to the overheating. It seems like it happens when you have the cpu working hard only.

You might not be able to do a scan, since the pc will probably shut down. Clean the fan with a brush, don't use a vacuum cleaner, it might cause static electricity and cause other problems. You can use the v.c. from outside and clean the fan's filter with it.

My pc always does this when the fan needs cleaning, it is not able to run PS, and shuts down... Time for spring cleaning...