I just got a g5 1.8 single processor that didn't have a hard drive, so I bought a maxtor SATA II drive and was planning to load the os from dvd. The mac starts to a flashing power button, what could be the problem? That's as far as it gets, no screen, doesn't recognize an apple keyboard/mouse, so I'm stuck there. Please help.

Just make sure that you have connected the power on the hard drive.