I would check that things like SSD's, Ram sticks, motherboard connections are all tight.
After that, we can diagnose things. If you want a memory tester, just download Memtest86 to an extra USB and boot from that, that will tell you if it's a RAM issue. There are many SSD checking softwares out there, I don't think you'd have a problem with that. If none of those show any signs, then things may be a bit deeper. The things left are the CPU, Mobo, and PSU. Each of these are hard to test and require replacements to pop in and check for stability.
Memtest86: https://www.memtest86.com/
This sounds like a tough problem so I wish you the best of luck
- Ethan