Thanks for replying.
Sorry—It's a desktop PC and I actually did mention that the keyboard and mouse are USB.
The problem hasn't happened in a couple days so far...but I just re-read my original post and realized I could've simplified the explanation by saying that sometimes when the screen goes off (in power-save mode) I can't get it to come back on because the keyboard and the mouse have somehow disabled themselves (indicated by no lights showing on either). But the PC itself looks and sounds like it's still running (fans going, power light on, etc.)
Thanks for any help—specs posted...