100 amp main fuse keeps blowing

I have a 2000 mazda 626. Just put in a new battery and new alternator. Took it to Walmart to get the oil changed and drove home. when i went to start the car again later, it would not start. I replaced the main 100 amp fuse with a 100A fuse and when I went to start the car the fuse blew. I tried 2 more fuses and they also blew. Any help would be greatly appreciated.