Peugeot 405 Diesel

I have a 405 Diesel Mod 98. Ultimately it costs a lot to start and when I start driving the engine stops. The mechanic already changed all the hoses that carry diesel, the spark plugs, put some bosch, twice the filter and tamien we put injector in the tank. The car continues to fail, what could be the problem? If anyone has an idea of ​​what happens please tell me, because the mechanic does not know what it can be. Thank you