I've checked event log etc. If this helps, some programs that run in the notification area have occasional animated icons; when I must restart the computer those notification icons stop animating they stick.
I was asking about the event log to understand if there is a report of something crashing while these processes are running, like a driver or a PCI resource conflict. Have you added or changed hardware since this issue raised?
When download a large file or backing up my computer, it's typical the computer restarts; if this information helps ?
It could be the network adapter, see if you can find a tool to make a specific diagnostic of it, as suggested before. However to be sure about the integrity of the card you should test another one or, if attached to a PCI interface, try to move it to another slot and see if it makes any difference (in case of resource conflict).
I don't know what to do with a downvote, downvote if you want, but explain me what's wrong with my answer, otherwise I cannot improve. Thank you!