why vectra 1.9cdti life 2008 take long-self to start?

changed camshaft sensor. battery and set the timing by the mechanic but spanner sign still on.
I have been few other mechanics they all suggesting different parts & sensors. .one the mechanic said that it is bottom crankshaft's pulley which is damage and timing bit out that the reason camshaft sensor showing.
Does bottom Crankshaft pulley coursing the problem?