Lately I've been having a problem where after my machine has been running for a few hours, all processes will suddenly become extremely laggy, and the cursor and other UI elements start flickering. However, task manager doesn't register a high load--<5% cpu use and ~14% memory. Core #3 does seem to be at about 30% consistently though. MSI Afterburner registers an unusual 15% load on one of my two GPUs, however this load doesn't show up as attributed to any process in Process Explorer. Regardless, this shouldn't be enough to cause problems. My machine is pretty new and very high spec, so I'm surprised to be having lag problems.
CPU: Intel i7 3930k OC'd to 4.0 Ghz
GPUs: 2x EVGA GTX 480
MB: Asus Sabertooth
Through trial and error I found that killing dwm.exe gets rid of the lag, but not the flickering cursor/UI. Obviously it also disables aero so I'd rather be able to leave it enabled. dwm.exe doesn't register as using high cpu, gpu or memory in task manager or process explorer when the problem occurs.
I've done a scan using Avira and it came up clean. Any ideas would be much appreciated.
Try turning off all the windows effects (rightclick my computer > properties > advanced > performance > untick all the box's), and see if you get any of the symptoms you had before. This way you will know for sure if its your windows aero.