I have been an active boinc runner for years. All is ok till the last 2 weeks, suddenly most of the boinc file make my computer kept rebooting. It is like the pc is overheated due to high computing load. Is there any changes to the processing file lately?

More to the point, when was the last time you opened the computer up and removed all the dust from filters, fans and heat sinks?
That's something you'll have to do periodically to allow the computer to breathe and disperse hot air in a normal fashion.

---

Well as the computer concerned seems to be a laptop that may be difficult. Though it will be worth checking that any fan duct entries or exits are clear

Couple of suggestions, don't use the INTEL Intel(R) HD Graphics 4000 to crunch, many people here have found it negatively affects the CPU crunching, and will of course add more heat.

Also with a laptop crunching SETI@Home I would always use some sort of cooling pad.