It doesn't see the new drive if you hold the option key at startup, or select it as the bootup disk from the install CD?
If you have the original disks, one should have a hardware test CD. You may have a bad logic board, processor, or bad RAM. Try testing your memory with memtest
http://www.memtestosx.org/
__________________
Power to Burn.
At speeds of up to 733MHz,
The most powerful Mac in history
burns CDs, burns DVDs, and
burns Pentiums
- apple website, oct 4, 1999. advertisement for the powermac g4