ok if u have flash 8 do this...
click.... modify>document> then click the box that hasa white square in it
this is for the background of the file
for anything else make sure the layer is unlocked (duh) then make sure all gaps are closed
make sure the color of the pain bucket isnt the same color as the background color(duh)
make sure you are in the right layer(duh).
if none of this works just try closing flash and restarting your computer........
if none of that works just back up all your files and uninstall it and reinstall it (this may require actualy having the purchased product)
good luck