Barking nonstop

my dachshund mix barks nonstop. how can i get him to stop?

It might be a too obvious answer but have you tried teaching the 'quiet' command?

um no i havent. i guess its my fault. i didnt train him when he was a puppy. i didnt know how.

he barks 24/7 ?????

It's never too late to start. It's quite simple but needs lots of patience. When your dog is barking give him the command you want to use to quieten him, I use 'quiet' but you could use anything you want e.g 'sshh'. At the same time I give a hand signal (like you've got your hand in a puppets mouth and you're closing it). The split second your dog stops barking reward with a treat and praise. After a few times I'd count to 2 after giving the command before I rewarded. VERY gradually the amount of time can be increased until eventually you have the result you've been looking for.
I may not have explained this very well and there may well be people that can offer better advice/strategies for this, but this worked for me and my girl. Best of luck.

It sounds like he needs a bit more than a Quiet command if you haven`t trained him at all.
Establish a routine for him that includes two walks a day with off-lead running for part of it. This will help him de-stress.
Start a training routine - read Jean Donaldson`s The Culture Clash or Pamela Dennison`s Dog Training for Dummies.
Play with your dog - but use the play as a way of teaching him. Finding games are better than tugging games.
When he is barking, ignore him. When he stops, reward him.