It sounds like your car is in "limp mode". There are several reasons why this might have happened. To avoid throwing a bunch of parts at it and hoping something works, not to mention running up the $$$$$, it would be best to retrieve the fault code.
To get the code you need a scan tool or have the scan done at a shop, they'll charge you though. You can pick up scan tools at most auto parts stores. There are several brands out there, Innova is one. Google Innova to see what the tool looks like. They are easy to use.
Once you get the code please post it here and someone will suggest your next step.