Here I have Acer 5750G laptop with core i7-2670QM upgraded CPU for three years
~Two weaks ago I had first instant reboot. Now laptop can work 15 minutes or 15 hours as well with very different load (like games, or simple Firefox with music). It reboots with no BSOD/Minidumps (Sure, they're turned on in PC Settings). In event viewer are only Critical Error Kernel Power "System had unexpectly shut down". Airflow is normal, no debris, cleaned up weak ago (with full clean of holes and fan) and there are normal temperatures both CPU and GPU. Reboot is like this: instant shutdown, 3-4 seconds without any activity, power up. All drivers are up-to-date, no new Software/Hardware were installed 2 weeks ago. Interesting thing, that with some delay before restart if focus is on text edit field, in this field appear symbols like "0x,.klop-". I have "< ," key broken, but I can press it. Now trying to repeat error with special press broken key. But nothing. It reboots still randomly, but maybe when I press it, don't know now.
So, question: can keyboard cause this "hard" restart? I see that these letters above are in same region of keyboard. Should I buy new keyboard?
Memtest86+ tests passed, sfc and chkdsk both drives are OK. Using Win 8.1 x64 Pro, Antivirus: AVG.