Laptop Shutting Off

I have an issue with a Dell Inspiron laptop. Computer was running normally then shut off, now it only comes on at random then quickly shuts off as if the power was pulled. I've tested the following:

• A/C adapter reports good via multimeter and charges the battery normally
• Battery is weak but still holds a charge confirmed via BOIS, no change if the battery is in or out
• RAM is good, been tested, removed and replaced
• Cooling is good, CPU cleaned new thermal paste applied
• Fan, seaksink/heat-pipe assembly removed and cleaned
• Dust removed from inside case

My initial thoughts were overheating. Those thoughts didn't hold up when the exposed underside of the laptop was directed at a fan blowing air from the A/C to into the laptop it'd still shutdown at random. I'm now thinking there are there is an issue with the motherboard age and/or wear/tear over time or even the CPU. The laptop is about 3 or 4 years old. I don't happen to have a spare CPU or motherboard for this machine or I'd test further to confirm my thoughts. Anyway I thought I'd stop by here and get some second opinions, thoughts or suggestions before I retire this laptop.

Thanks!

 

Thanks, I wish it were software that's an easy fix. It's hardware alright. It even shuts off if I leave it running at the BIOS long before it ever gets to boot the OS. Thought I'd post out here just in the off change it's something someone ran into before that I'd not yet seen.

Unless something comes to me by morning it's time to go Black Friday shopping for a replacement lol. I suppose if it had to die now is as good a time as any. All data on the HD is still available and secured which can be quickly imaged over to the replacement.