MacBook Battery issues...

Recently, my battery for my MacBook died on me. I had my mac plugged in, battery icon reading that there was about 3 hours left on the charge, closed it up, unplugged it, and went to class. When I opened it up in my class, nothing came up, although the sleep light was on, no button I hit was of any good. When I got home, I plugged it back in, where I then saw an "X" over the battery icon, and "No Batteries Available". I went to the Apple store where they ran a diagnostics check, which blatantly read, "Replace Battery". This didn't seem odd to me, as it showed my battery had been through 447 charging cycles, so I purchased a new battery thinking that that would solve the issue. However, when I returned home and put the new battery in, nothing changed, and my mac still reads "No Batteries Available". Any ideas to what is going on with my MacBook??

Two things to check (should have been done by the Apple store genius): The MagSafe adapter, and DC input board. Either one being defective could cause the problem you have. But first, try resetting the SMC to see if that get's things going again.