I have a 99 vw jetta and the battery died we disconnected the battery to get a new 1 but he key wont open the door how do i get the door open to reconnect the new battery?

The first link says you can disconnect the battery cables and touch the Pos and Neg leads together to discharge any stored charge in the system. I don't think that is good, it works on some cars and other cars it can short out electrical components. I think it is better to disconnect the battery and turn the key on and let it sit for more than 1 hour to reset the immobilizer. Just my thought.
This is Why Your VW Won't Start After a Battery Replacement ' VW Parts Vortex

Volkswagen Jetta no start and no power to dashboard - YouTube

Volkswagen Jetta no crank no start Troubleshoot & Repair - YouTube

You need to have the VW dealer or a well equipped VW savvy repair shop scan the body control module (or whatever VW calls it) and see what codes return, it is likely the problem, but hold on you can't jut pop one in it must be programmed for your car.

put the key in the door and unlock/holdover for 30 secs,then lock/hold over for 30 secs.then press/hold down the unlock button on the remote,you have juast reset the system........

all vw MUST be reset after battery dies/changed.put key in door,unlock/hold key over 30 secs(windows go down)then lock/hold key over 30 secs(windows go up/sunroof closes)then press unlock button on remote for 30 secs......RESET DONE......(try this for fun....sit in car after turning off engine/remove key,drivers door keypad is still live(until you open door)ALSO when engine is running lower any window and then raise up with fingers in top of door,the window will rollback.(if you do it once it hurts..twice it really hurts..three times it traps your hand in.)ALL THIS is NOT in the handbook.......

using your remote key fob push the unlock button or use the key in the drivers door and turn it to unlock

Try removing Neg (-) cable wait a few minutes replace cable and see if it resets.

Check the fuse box for a blown fuse.

sounds like the latch on the door is going out. $350 to fix. try turning off the alarm with the key by openning the trunk.

Tips on how to safely get into our beetle VW 1999 because our key locked inside and the battery died as well.

I have a Jetta 2005 and I just noticed that after this:
when my battery died after 7 hours playing my stereo, then I charged it for 30 minutes and my car could start on again. After that incident thet remote key started failing when I push the open button twice to open all doors. They remain closed, only passenger door open. Then I disconnected battery over 15 min to reset computer, and the clock and mileage gage remain on all time after that. Never remain on before it was disconnected and conneted again.