1997 Chevy Lumina won't strat

my chevy lumina won't start i turn the key and nothing. have tried to boost batt., checked all fuses,charged batt.. I have crossed the terminals on the starter and it cranks that way. I was told it was the key and the dealer told me it probably isn't that i should have the codes checked. all lights work and all guages work have tried it in neutral as well and it still won'tstart, any ideas?