new hard drive

I have an aptiva that hangs on the aptiva screen.
I put a new hard drive in. When I F1 and enter setup. It reads it correctly as 40 gig its a PII, 350 MHz, 128 memory.

I booted to Won 2000 prof disk installed the OS fine.
However on the next boot it reads insert boot disk and press enter. I put in the win 2000 disk and it boots up fine into win 2000. I take out the disk and it gives the same insert disk message…what did I do wrong
jan