Q: Not Starting power disconnecting

I just got a new battery for my probe and it ran very well for 4 days. Then I thought the battery died. My meter read 12.7 – 12.8 volts and sometimes the car would have enough power to run the fan and dash lights, but it doesn’t start. I can hear a clicking noise when I try to start it but that’s all. There is no cranking happening. There is some play with the key ignition in acc/on position. When I open the door the beeping quits. When I step on the brake I hear a click. It seems as thought the power is being disconnected. I have been looking for things like corrosion on the lights and checking my fuses. I can’t figure this out. I was told unplugging the brake switch might help stop the draining. Do you have any ideas about this on how to fix it?