What is the problem

Hi,
My 02 Elantra has manual transmission. When I step on the gas as the lights turn green, it won't accelerate. I shift to second and same thing. I shift back to first and everything will be fine. Has happened 4 times and every time at the lights without any tell tale signs or warnings. I can never know when it's going to happen. One other thing. This would also happen randomly when the engine is cold. I turn the ignition and the engine won't start as though the battery is dead. After shifting the gear from low to high, back and forth a couple of times, it will start like new. Does any one know what the problem might be? Thanks.

Hmm, maybe some sort of clutch problem? The starting problem sounds like maybe you don't have the clutch pressed far enough down to the floor. It won't let you start the engine if it's not all the way disengaged. If it's not that I don't know what it could be.