My Zelda game won't save, as soon as I turn the game off and then reboot the system its gone.

well, when you erase a game file from an n64 cartridge, the file itself is not erased, all that happens is the game marks it as an empty file and available to use; but all the bits and content that make up your saved game file are still there. It may just be the system is having a hard time reading the data stored or is failing to recognize it.

You cannot save after you have beaten the game. Once Ganon is defeated, the game is complete.

To save the game without dying, press A + B + Start + Select. It will give you the choice to return to game or to save and quit.

there should be a delete save game option somewhere on the main screen. it shouldn't be too hard to find

It sounds like the internal battery is dead or the use of too many gameshark cheats.

delete the whole game of zelda and redownload

While online, goto the manufacturers web site and download the manual

To save you should be able to press start and go down to the save button on the bottom of the items menu.
Press L or R to scroll to other menus if you aren't already at the items menu.

If you are unable to save, it may be due to the battery within the game having run dry.
This is a common issue with cartridge based video games like Game Boy Advance ones.
However for you, this may not be the case.

It's known to be a really great game. Have fun.

well you can go to the options..that should be there and go delete. Or you go to start and you select new game and you start playing again and then you go to save blah blah blah blah and then it should ask are you sure youwant to overwrite file and you say yes and vwaila it should be solved!!! another way is to mess it up so while your saving your current game it should say dont touch the power button or something well turn the game on and of 7-8 times and it should mess it up enough. this might cause other issues though so....up to you.

some n64 games do that, call nintendo