If you have the same battery that sat in the car all Winter chances are it's pretty much toast by now--even if it was new last Summer/Fall. A battery with low charge will let the car crank, but if it doesn't have enough power it won't get the engine to turn over. If the battery has tested out o.k., have it tested again as those tests are often not accurate. You've probably looked into this thoroughly enough by now, just thought I'd mention it if none of the other suggestions here worked...