HELP! Volkswagen 1997 Jetta running/starting problems!

Hello,
Im here because I have a volkswagen jetta 1997. Purchased it two months ago, with about 150,000 miles on it. The car ran great all the way to the house. Had to do some work on it with the power steering lines, and got a new fuel filter. After the work was done, we drove it around the block and then thats when it first stalled out. Hasnt been running since. Just recently been trying to charge the battery up and it says the battery is charged but still nothing after it turns over!
Today, in the morning, the car started up with no problem, then itll stall out. Then later during the afternoon, it turned over like it usually does, and nothing more happens. Then, in the evening more, it started right up again and stalled again!
I have noticiced when it decides to stall, is when it reaches the temperature its supposed to be at (normal). This all doesnt make much sense. & i have no idea what it could be. Thought maybe a sensor of some sort but, really, have no clue.
PLEASE, HELP! ASAP!
Thanks!