Hi, Ntina_poulop and the usual suspects are:
1. Fouled spark plugs.
2. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
3. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
4. Loose connection at ignition coil or plug between ignition sensor and module.
5. Spark plug cables in bad condition, shorting / leaking, spark plug cable connections loose.
6. Faulty ignition coil or electronic control module or CDI box.
7. Faulty CKP, CMP, or BAS sensor.
8. Faulty ignition switch.
9. Tilt sensor needs a reset.
10. Security alarm failing to disarm needs reset
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
Sym Citycom won start 1200km
Piaggio Won start
SYM Citycom 300i User Manual