B&W G3 Suddenly wont turn on

I was upgrading the HDD in it. After installing and updating 10.3.9 I shut it down and put the old HDD in to get files off it. The mac then gave me a message saying that I needed to restart the computer, so I did, and it gave me the message again. So I pulled the old HDD back out thinking that I just can't do that on a mac.

After that it doesn't turn on at all now. Is there any way of fixing this?

So I figured it was dead for good and found some buttons on the motherboard that I decided to push of out curiosity. Now it works...

What exactly did I just do?

When you changed the drives how were the jumpers set? The old drive was probably still set to master. Set it to slave and it should work.

The two buttons, one is a reset and the other is a power button.

Reset the power management no doubt from your description, which restored to default. If you wish to get files off the old drive, do as cradom suggests and install as a second dricve with jumpers set to slave.

Go to the web site of the drive manufacturer and you will see the settings.

The way I had it set up was I had one HDD set as master on the primary IDE cable because it only had one connection on it. The second HDD I put as master on the second IDE cable and unplugged the DVD drive. I assumed it would work the same way as a PC.

Do I still have to have the second HDD set as slave even though it's on a different IDE cable? I was thinking that the problem was the mac not knowing which device to boot from. Is there a menu I can bring up to choose a device maybe?

If you hold down the option key while your computer is starting up (the grey screen before the apple logo appears), you will get a menu asking where to start up from. Also, from inside Mac OS, if you go to system preferences and choose startup disk, you can set a specific disk to be the default startup disk.