I did a new build with a Coolmaster Cosmos case, Wofdale 8400, Gigabyte ?? MB, etc etc.
Every few days when I jiggle the mouse to wake it up, the CPU fan, motherboard lights and everything
will start cycling (come on for 2 sec or so, then go off for 2 sec, then on for 2 sec etc etc) it will continue
indefinetely until I turn the PSU off at the back and then turn it back on and reboot, then everything's
fine for a few days......
First thing I'd do is do a CMOS reset, followed by a "Load Optimized Defaults" at the first reboot. If you need help with this - post back; if you get it done, and the problem persists, post back with make & model numbers for: RAM, power supply, motherboard, etc. Also - do you have a case speaker plugged in? (I know your Cosmos didn't come with one, 'cause I gots the same one - best damned case I've ever seen, much less owned - planning on about three more of 'em... )
This happens on a good number of boards and it's happened to me on several. I have an Asus P4PE and, more recently, a Gigabyte GA-EP45-UD3R, which do this from time to time. My "fix" is to simply do what you do and that's to turn off at the PSU and start it up again. It's fine from that point on for weeks or months until it happens again.
To me, this is just a quirk of nature that happens with "good" components as well as "bad" components. While you might be able to ultimately track it down to the individual item causing the issue, more often than not it's an exercise in futility.
I suggest shutting down completely for a week instead of suspend or hibernate (if you are using those modes). Just to see how it reacts. Also, you can shut off the "wake on mouse move or keyboard press" and start by using the power button on the case, also to see how it reacts.
Sometimes modifying our behavior is the only solution!