Funny story and some questions about ram compatibility and new CPU

[PapaXpress]

A memory leak can do this. Running out of drive space can do this (cannot cache as needs require). Not even memory can do this (lots of caching). Heat can also degrade performance (and burnout a CPU). A bad power supply can cause all sorts of intermittent problems (but that does not seem to be the case here).

If you boot into safe mode does the general laging go away? If so it could be a bad device driver (notorious for leaking memory). Or perhaps it could be a service or application which is run during startup and leaks (use CCleaner to see what is starting up with windows... or even better Game Booster).