that wasnt meant in a mean way. just saw i forgot the smiley..
do all the things i listed.
its a start to make sure those are not causing it.
after that we can limit it a little more to software your running (very small chance its hardware caused).
if its a warning for disc space, the c-cleaning should help (turning off system restore,reboot, turn on again might help free up more space), if its low mem space (ram) it might be caused by software running (wanted or "unwanted").