This has been an ongoing issue for a long time, based on web searches I have done (such as the one that led me to your question). Unfortunately, everyone has questions and nobody has answers... or at least, not anything that fixes the problem. It's only the mouse and keyboard that are affected. Other USB devices work just fine. I have to assume this is some kind of software incompatibility or bad update, but nobody seems to know what. Brand of mouse/keyboard doesn't seem to matter. The only common threads as far as I can tell are 1) Windows 7 (always 64 bit, often if not always Pro), 2) it only seems to happen when you're in the middle of something intensive (for me it's games), rather than just streaming video or using Google or suchlike, and 3) turning the computer off then back on always fixes it (until it breaks again), but rebooting doesn't always fix it.
If anyone has an answer to this, PLEASE post it. There are so many people having this problem, I find it hard to believe that the issue hasn't been identified and fixed somewhere.
Things that haven't worked: * Reinstalling the drivers * Removing the mouse in device manager, then reinstalling it * Changing the power settings so that the USB port doesn't turn off * Changing to a different mouse or keyboard * Completely reinstalling Windows * Installing a new motherboard and CPU * Upgrading to a more powerful PSU