I was just working on my truck today and when i turned it on white smoke came out of the exaust and now the car wont start anymore. all i did was change the belts and the spark plugs. should i just asume the truck is done for good or is there something i can do to fix this problem. any advise would be greatly apreciated.

if the white smoke from exhaust of car is noticeable even when the engine is hot or at all times, then your car is experiencing a blown head gasket.

Head gasket is a seal located between the cylinder head and the engine block, the purpose of the head gasket is to keep the water that circulate to cool the engine from entering the cylinder head. If this water is not prevented from entering the cylinder head, a steam is formed which in turn causes a white smoke from exhaust of your car to comes out.

White Smoke From Exhaust of Car During Starting (http://www.cartechhome.com/2008/02/white-smoke-initially-comes-out-while.html)