what is the problem with my citroen berlingo diesel engine?

after replacement of the fuel filters my engine does not start as it used to.After standing for a few hours I have to try and start it many times before it catches.Sometimes it catches but seems to run on less than all cylinders.after switching off and restarting most times i get back to all cylinders working.when I have the problem starting I get thick smoke from the exhaust.The vehicle is a Citroen berlingo model 2001