Setting up 2nd router as access point

Hi after reading through various online guides about setting up a 2nd router as an access point i have a few questions. First things first i did attempt this before and it worked but after the wireless on my original router began to go out until it eventually broke. i don't know if the this is connected with setting up an access point. I realize now i did not set the routers on a different channel and the SSIDs were different. I have a new router from AT&T and i want to try again to set up an access point. my question is what should the settings in the 2nd router page be. Does the name of it and password need to be the same? And also is it possible that setting up this access point will break my original router?

Thanks in advance