Prestonfitz is right a scan tool attached to the diagnostic socket under the dash will most likely reveal what is wrong. The computer in your car is going to have relevant information stored in its memory which will help figure out what is going on. A scan tool is needed to retrieve this information. A professional grade scan tool allows key engine sensor data to be analyzed right off the scan tool without having to do intrusive testing at each sensor.
Unfortunately there is not much of an answer that I think can be given at this point, with the amount of information that is supplied here. Fortunately, this is something that can be fixed. I would recommend taking the vehicle in for service as soon as possible for diagnosis, preferably to a shop that is proficient in dealing with the diagnosis of VW products.
All drive-by-wire cars (starting from 1995-2013)has an EPC light. EPC stands for Electronic Power Control which is controlled by the ECU (Engine Control Unit). This is a computerized hardware device with software to control all sub modules in the car that is connected by eother OBD II or Can Bus. Any input from these modules can activated the EPC circuit especially if the reason for sending its signals to the ECU, couldn cause damage to the engine. For example, if the car runs out of oil, or if the emisions exceed the prescribed level ect.... This will activate EPC, cut power to the engine (limp mode). See EPC solution at http://volkswagen-polo-highline.blogspot.com