What happens when timing belt breaks?

If it was a broken timing belt, the engine would not run. The timing belt or chain connects the crankshaft to the cams. Without a connection, the cams would not move the valves. --- You could remove the spark plugs and look at them. If one looks different, look in the spark plug hole to see if there is any visual clue to the origin of the noise. Spin the engine to see if all the pistons are moving.

may have swallowed a valve,

If the t belt breaks on a 1.8 you get to spend $$$$$ it's gonna be expensive,these bend valves when the belt breaks,just did one on a Jetta about two weeks ago.When your mechanic advises you to get the belt service done ,it is advise well heeded every 105,000 miles on that model.

my timing belt broke a while back in my 90 with a 2.0 i ended up having to get the head rebuilt because it bent 9 out of 16 valves and damaged lifters. all total it cost me $510 to get it rebuilt and i did the work of getting it out of the car and back in

If you wereren't using your car frequently or had stopped and started it quite a lot, it is quite sure it must have been the timing belt. As others have said this reparation is costly. In this article you can find the explanation if it was a timing belt http://motor.onehowto.com/article/how-does-the-timing-belt-break- 729.html

When I try start the car sometime won't; I driver it for 15 start getting very slow

I am not expert mechanic, but just did replace TB, because I was afraid by one of mechanics, who told me to do. I had volkswagen Jetta 2005, 115k miles. The reality is it may be scam, be careful, because after replacement, there was nothing happened in my belt, and it looks like new and as strong as it is and its factory product which i believe better than off market TB parts. I think Factory TB easily goes 150k miles in normal condition.