want to guess what problem my car might have..

I was recently in an accident got my car back from the bodyshop
all new parts installed, new radiator, new condensor, new fan assembly.. it was dark it looked like all all t he wires etc were connected, pipes etc.. i have a problem though.. i notice that theres smoke coming from where the manifold cover is..white smoke after driving for 10-15 min
i also noticed that the radiator fan isnt spinning..
i thought the engine was overheating but when i look at the dashboard i see that the needle is perfectly between H and C.. right in the center
i touch the radiator cap extremely hot.. so i wait for a bit.. open it up i see theres enough water etc..so im wondering.. what the issue could be.. i mean if the engine was overheating needle would show it.. but am i worrying that the fan isnt spinning?! also sometimes when in drive it slightly slightly jerks.. and goes forward.. maybe bad spark plug? i or bad motor support? anyway i could tell ?

ITS A NISSAN ALTIMA 2003 4 CYL 2.5L

Please advise

thanks again!!