You can download flash for linux directly from Adobe:
it has been in pretty good working order for years now. Get the tar.gz version, not a .deb package. I believe this installs via firefox.
If not, untar/unzip it:
tar -xzf thefile.tar.gz
go into the directory this creates and read the instructions.
This should overwrite your non-functioning version -- just remember that you did, because debian will still think it's the package, so don't use any more apt commands on it!