2003 Granda AM won't start

my 03 grand am v-6 wont start. its acting as if i have a dead batt. however i know the bat is good. turn key over & get nothing. nothing electrical works. problem started two weeks ago. everytime i started it it would act as if the batt was disconected IE: clock would reset to 12. now its completely dead. have a clicking sound coming from speakers that goes away when i step on breaks. any ideas on what it could be? thank you!

I would suggest to check all the connections battery cables make sure they tight and clean, The wires on the starter also they can get dirty and make bad connection. there should also be a power wire goin to the fuse box n ear the battery. If none those are a problem i would think maybe your igniton switch . Do your headlight turn on manually ? But by your clock reseting it seems to b a poor power connection somewhere. Or a wigged out battery have u tried swapping battery or havin a load tester put on it?