Hi
If your system restarts whilst installing an OS, it's a hardware problem -> usually RAM.
Since you've eliminated it to some extent, run these RAM diagnostics to make sure what it is.
For RAM:
Windows Memory Diagnostic Tool and
Memtest86+. (2 hours each is OK)
Run them with 1 stick of RAM in each slot separately during both tests. It will take a while but to me, it seems one of your lots is faulty.