Did you try it with the cover off and have you cleaned the insides recently and one last question. Did you replace the heatsink compound on all heatsinks?
Recently, my computer decides to shut off at completely random times. When I turn it back on after it shuts down by itself, it displays a c000021a error after the logo load (doesn't matter if I try to boot into Safe Mode or not). But when I reboot it again, everything runs smoothly and I get no significant problems whatsoever until the next time it decides to crash out on me. The times when the computer crashes are completely random; it may happen once every other day, at other times it shuts off multiple times a day. It's honestly frustrating to lose work whenever it shuts down and all the things I've been trying to get it fixed for good doesn't seem to work at all.
I've tried using Last Known Good Configuration, but it never solved anything. I tried to use Windows Repair multiple times; sometimes it finds the error and "repairs" it, other times it detects nothing at all. I have no recent System Restore points so I can't go back to when this problem never existed if I wanted to. I tried uninstalling any recent installs that might've triggered the issue but nothing worked. I'm not sure if it's the work of viruses, but I tried scanning my computer with anti-malware programs like AVG and Malwarebytes just in case but nothing came up.
Is it even possible to get rid of this nuisance without having to reformat my computer?
Here are my specs for reference:
Windows 7 Home Premium 32-bit SP1
Intel Core2 Quad CPU @2.40GHZ, 4GB RAM, NVIDIA GeForce 7350 LE