If it works fine without sim card and restart with sim card then 99% your problems occur when the module tries to register into the network and it consumes high current from the power supply. If your power supply is capable to deliver 2A continuously that does not mean it is capable to withstand the 2A spikes when it registers.
Check with an oscilloscope the power supply pin when it registers. Most probably the first spike when it registers will drop the voltage below its minimum working voltage and that's when your modem dies. You will need a digital oscilloscope to clearly see it, with an analog oscilloscope it will be very hard. Two possible causes: first, bad capacitor at power supply (what capacitor do you use and what is the voltage?), second, bad antenna circuit (high vswr), and high vswr usually means high power consumption. There is also one small chance that your module is defective, in my experience, sim900 is one of the worst modems. sim800h is much better.