Most of the times I've had PCs shut down, it was bad RAM. PoF uses significantly more RAM than GW2 did before. GW2 may be hitting a stick of RAM that has not otherwise been getting stressed before now. While no software RAM test can be perfect, Memtest86+ has not been supported since 2013, has known problems and should not be used at all. The original Memtest86 is now being supported by Passmark but is not as good as the others. HCI Memtest is the best of the "Memtests", and should be run with as many instances as will fit in available memory (for example, if you have 16GB RAM, run 7 instances of 2047MB each). Finally, the best choice is Google Stress App (GSAT); I have linked how ASUS prefers RAM to be tested with GSAT. I'll quote ASUS on HCI Memtest vs GSAT: "The Windows version of HCI Memtest is a good test for hammering the cache and memory simultaneously. Googlestressap is more memory focused and picks out memory related errors faster than HCI Memtest does." GSAT should be run for a minimum of an hour. An overnight test of 10 hours with either HCI Memtest or GSAT is best to declare RAM or motherboard problems to be extremely unlikely. I have also seen unupdated motherboard BIOS and chipset drivers cause RAM to act bad until they were updated. If you look at changelogs for PC BIOSes, they often consist mostly of "improving RAM compatibility". If you have never updated your motherboard's BIOS or chipset drivers, you may want to try doing that, especially if the RAM tests only throw errors very rarely.