Don't worry!

First: write exactly which firmware you've taken (choosen).

Search for the right fw (should be the latest - http://oleg.wl500g.info/1.9.2.7-8/ )

Then use tftp to flash your new firmware, but pleeaaaase: wait some minutes more after flashing and use just a wire connection.

Follow exactly http://wl500g.info/showthread.php?t=10989
but use the name of your fw instead of tomatoxxxx.trx

If that fails, there is an other possibility to bring him back......
But I have done it several times and it always worked.