When you try to start it does it click or make any kind of noises?
Headlights come on?
First thing to check if you are sure the battery is good is the battery connectors and cables. Make sure they are tight, clean and there is no breaks in them. Especially ground cables. if the cables are loose, you may still get power but not enough to start, even with a jump.
If those are good, check main fuses and fusible links.