Volkswagen Jetta 2007 1.9 TDI can't start. Solved! 

Actually there were 2 problems - the timing belt and the glow plugs relay.
I have problem with my car - Volkswagen Jetta 2007, 1.9 TDI, 105 hp, engine code BXE, 5-manual transmission. Sometimes I can't start the engine. No matter is it cold or warm. Sometimes it starts from the first time, sometimes I need to crank it more than 10 times. My car mechanic checked the glow plugs, the battery, the starter, the fuel filter and all sensors for problems or short circuits... Everything is working fine! When the engine starts, everything is perfect. There are no strange noices or vibrations or something disturbing. I can drive the car safety and for a long time. When he checked the car for errors it says that sometimes there are no 5 volts to the relay for the ECU. He checked the immobilizer and the key, but they works fine! And nobody knows where is the problem... Soon I will go to another mechanic who is electronic specialist and I hope we will find the problem!