I recently acquired a broken Macbook from my girlfriend's family and I am trying to get it in working condition. She managed to get a free replacement as a gift before getting the other broken one in working order, but before this happened they took it by a mac store and had it looked at. The mac store said that the only issue with the computer was that the hard drive was broken and needed to be replaced. I would return the macbook to the store to have it looked at again but the nearest store is a good 2 hours from where I live, so that isn't very plausible. I replaced the hard drive with a new 400gb part, and upon trying to get it to work, the computer won't boot up. All the parts that I touched (which isn't many as I assume you all know from changing hard drives that it only requires removing the battery and a small L-bar in the casing) have been replaced, and I was grounded and very careful for static. The Macbook connects to the wall, the power cable will charge red for the battery and green on the actual plug. The battery check has power as well. When I press the power button on the laptop it doesn't even try and start. What part is this probably a problem with (If you all could give me a few possibilities if its not one thing definitely) and what would it cost to fix? Thank you!