You don't state if he was playing ECO with no problems prior to the upgrade so I will assume that he was.
I would start by watching the heat of the CPU and GPU as well as making sure that the PSU has enough power to run everything at max. A lot of newer computers will power off if they get to hot, I have had games like ARK, cause a reset when the graphics card got too hot, ECO is more optimized than ARK but has Far more calculations to keep up with. Also if the PSU gets overloaded (components drawing more than its max power) that can cause a reset too, there is also the possibility that he has a faulty component, just because it was new doesn't make it 100% working.
He could also try putting the computer back the way it was and see if the problem is still there, if not, then upgrade one piece at a time until he finds the part causing the problem, but my guess is over heating or the power supply is too weak for what he has.
Games like watchdogs and The division are not really a good comparison to games like Eco, the environment of those games isn't as demanding on the RAM and GPU as they don't have destroyable worlds, I don't know about unturned as I have never played it. ECO does have a 100% destroyable world, as a result there are a lot more calculations that must be maintained by the computer also the amount of the calculations will changed based on what is loaded in the "chunks" that are currently loaded, an area of the map that has not been touched by a player will have far fewer calculations than a chunk that has been leveled out and has 10 factories making stuff.
I have players who cannot connect externally. "Failed to establish a connection - no response from remote host". When using a webbased port checker, port 3001 is listed as open. The web panel works. However, 3000, the default game server port is closed.
Currently, inbound entries exist for both TCP and UDP in Windows Firewall. Each with a range of 2999-3001. My AT&T uverse modem has one TCP/UDP entry with the same range. Avira Antivirus is installed, but uses Windows Firewall. This configuration, despite port 3000 being deemed closed, has sometimes allowed brief connections of 30 seconds or less by external clients. One player connected on their first attempt, dropped, and has had no success since.
Troubleshooting has included running the game server with ports 4000 and 4001. With netsh running on the machine with two entries for forwarding 3000 to 4000 and 3001 to 4001. With this in place, both 3000 and 3001 were open when checked with Canyouseeme. Unfortunately, attempted game server connections failed. Netsh entries have since been cleared and the server's ports have been reset back to default.
Server Network Config
Public Server: True
Thank you for your time.