Not Exactly A Crash More Like Epileptic Fit ?

I have had a refurbished DELL INSPIRON N5110 cpu i5 2410M 2.3 GHz
6 Gb Ram Windows 10 64bit 500MB HDD. Possibly BRAND NEW Returned to Dell with a fault they could not find and resold as refurbished. Worked perfectly for 1 month then THIS ( SEE VIDEO ) happened. To stop it I had to hold down start button for 15 seconds. It restarted straight away and did not happen again for another month. over the years this became more frequently, weekly, daily, and eventually about 1 month ago it was happening every 1/2 hour especially if rendering Videos. Last week I decided to re-format HDD and re-installed Windows 10, as other strange things began to happen such as the CD ROM Drive clicks and tries to load even though no cd present and door untouched. Also the computer would not SLEEP, SHUTDOWN nor RESTART, TO shutdown I had to use the Start button. This re-install of Windows 10 did fix the Start, Sleep and Wake up. BUT THE EPILEPSY continued every 20 mins, with or without LOAd. Temp is not an Issue as core Temps are both around 59 - 63 and the Fan and SINK appear to be fine. I replaced the Battery NEW for OLD one but mainly run unit on charger.
Failing this I purchased another Motherboard and fitted that Today. I cleaned Processor Heatsink and renewed compound with Arctic Silver 5 cleaned everything including Fan and all Plastic terminal connectors. Started up fine and required WiFi reconnect but then worked OK for 10 minutes before having another Fit. I will upload a silent short 7 second video of event but must mention that there is a very loud ZZZZZZZZZ noise when it happens. A computer friend of mine has asked me if the Graphics Card on this is separate or inbuilt in the CPU ? I don't know but maybe someone out ther may has seen this Phenomena and might steer me in the right direction. Thanks for reading. Cheers Andy . Thread won't allow videos.