Each time I get a new computer, the first thing I do, while installing Kubuntu, is to check the RAM hardware.
I once got computer that had 64 GiB RAM installed, but memory accesses beyond the first 32 GiB RAM led to crashes, especially in applications that have a just-in-time compiler (such as the Java VM or QEMU). So, now, my habit — that I recommend to everyone — is to check the RAM first.
How to do it
Directly from the Kubuntu installation DVD:
# apt install memtester
# memtester 50G
That will take a while, but will reliably tell you when the RAM is bad.
The memtester package is not on the installation DVD. But it's in the package repositories, fortunately, and that's why you can just install it on-the-fly.
