we have a 1999 Chevrolet blazer it will turn over but will not start, any suggestions?

Well there's countless things that it could be first off are you getting fuel? You should be able to hear the fuel pump humming when you click the key into the on position. also there is a valve on one of the metal fuel lines going in to the intake behind the throttle body remove the black plastic cap off of the valve and push down the rod in the center of the valve while the key is in the on position if fuel squirts out your pump is working. if that's not the problem check to make you have a good fire on your spark plug (also replacing or at least cleaning the old ones may be recommended depending on the condition I like ac delco # 14's ) another thing that would be good to check and also cheap to replace is the in-line fuel filter located under the truck on the divers side attached to the frame under the front. Pull it and blow through in the same direction that fuel would go throught it there shouldn't be very much resistance if there is replace it. That isn't everything that could be the problem but these are the easiest diagnosis and fixes. Hope it helped!!!

Three things are needed for a motor to run. take away any one and the motor will not start. Air, fuel, electric spark at the plugs. As Jdmuirhead suggested, make sure it is receiving fuel. Pull a spark plug wire and see if there is spark at the end of the wire when turning over the engine. Either use a reading device or hold the metal end next to a ground source to promote spark from the wire to the grounding spot. No spark? computer may need attention. Air should not be an issue. Also the computer may not let the injectors fire. Unless you have all the tools needed, have someone read the codes and it may isolate the problem.