Old PC keeps corrupting OS installations...what's the problem?

[Apepa]

It's my old PC from about 2010 which I replaced a couple of years ago with my current main rig. I have it set up in my bedroom for Netflix and running Steam Link.

Basically, every time I install an OS on it, after a couple of weeks the installation becomes slow, corrupted and unstable until eventually it won't boot. I've used Windows 7, Windows 10, and Manjaro Linux and they all do the same thing. I've also tried using different SATA cables, different HDDs, SSDs, and different RAM and it makes no difference.

I'm wondering if anyone has any suggestions as to what else might be causing it or easy fixes (like BIOS settings) before I take it down to the dump.

Asus M3A78 Pro
Phenom II 965 quadcore
GTX 560 Ti
750W PSU

Gracias!