I am using a USB Microsoft keyboard on my Windows box, running Windows 7 x64 Ultimate. Occasionally, key A is typed endlessly although keyboard is not touched (or other key is touched). I have tried another keyboard - same problem. I have found it to do it even with no keyboard attached at all (one time after wake up from sleep mode).
Unpluging and plugin again the USB keyboard is the workaround I use.
What could it be?