My 2003 cts will crank but the engine wont turn over it started this morning but wont start up again. i took off the gas cap and listened for the fuel pump and i heard that so im not sure what the problem may be.

Check the CPS (crankshaft position sensor). It is a common problem on the 03-07 cts. The car will start and run fine for a while but when you take your foot off the gas, like at a stop sign, it stalls and won't refire. Give it 20 minutes or so, long enough for the ecm to reset, and it will start again. Sound familiar? It's the CPS. Available at Auto Zone for 45 bucks. You'll need an E8 external torq socket. A 1/4 drive rachet with a 10-12 inch extension and a swivel adaptor will make replacement much easier. Also, if you pull the front wheel off and jack the car up a bit and open the hood to let light down into the engine compartment it will make it easier. This link will help...

http://s705.photobucket.com/albums/ww55/bw5234us/Crankshaft%20Position%20Sensor%202003%20Cadillac%20CTS/?action=view&current=2.jpg#!oZZ1QQcurrentZZhttp%3A%2F%2Fs705.photobucket.com%2Falbums%2Fww55%2Fbw5234us%2FCrankshaft%2520Position%2520Sensor%25202003%2520Cadillac%2520CTS%2F%3Faction%3Dview%26current%3D15.jpg

After changing the timingbelt on my cts the check engine came on and the car is so weak when i am driving it. to see what was the problem i took it to a shop and they found 4 cylinders are missing fire and i have other be telling me my fuel pump is bad.can someone tell me what could possibly the problem is?

You probebly need a crank sensor. take it to autozone and have them check the codes they will usually have a history crank sensor code. they usually act up after driving and letting set. the 03 cts uses the same engine as the later model catera. we have seen alot of crank sensor issues