92 Mercury Topaz with no battery power

I have a 92 Mercury Topaz and the other day it wouldn't start. When you turned the key you could hear the solenoid relay clicking and nothing would happen and when you tried to start it from the solenoid nothing happened either. This was right after shutting the car off for 1 minute at the gas station. It had done this before but then it would start up after adjusting the positive battery cable that was loose. That didn't work this time. I replaced the solenoid and now I have no battery power at all. Nothing comes on. Could I have hooked up a wire wrong? If so what is the right way to hook the cables back up? Could my battery be dead even though it was fine before hand (I unhooked it before changing the solenoid)? Is there anything else it could be or any way to test it to see what the problem is? This has been driving me and a couple other people crazy for 4 days now and any ideas and suggestions would be appreciated! Thanks.