Does the same thing happen without using the DSTT? In other words if you use a normal DS game does it still shut off?
If it works with a normal DS game cart, then the DSTT is faulty and you should return it for an exchange.
If it does the same thing with a normal DS game cart in, the NDS must be faulty. If you bought the NDS only 2 weeks ago then it should be under warranty, take it back to the store you bought it from (or return it if you got it online) and get a new one.