There are a few tricks you may want to try to see if it's up to the task. If your battery is really dead, often I find that it takes more than a minute for enough energy to transfer to the dead battery to crank the engine. Also making sure the clamps have sufficient surface contact to support a decent amount of current. The more surface contact you can make with the clamps, the less patience you'll need. But regardless you will need *some patience* . Only after you've waited a while would I try the ignition switch.