i took out a amp to replace it with a different one then when i hooked up the new one there was no power and then i tried to hook up the old on to go back to how i had it and it had no power either, what went wrong? blown fuse? is the amp that i was testing blown?

i did not disconnect the battery btw

 

go to radioshack and get one of those $9.99 multi-meters. check several points to see if you got voltage. could be a number of factors.
first thing i would check are the fuses.

 

check ur ground, even if it is connected, it might not be a sufficient ground