iMac Won't Start Up

[Blaine]

 Hope I am posting this correctly.

 I was trying to help a friend put a new hard drive in his iMac 400
slot loading machine, because the old one is making weird noises.
I hooked up an external USB hard drive and copied everything to
the new hard drive. That seemed to go as planned. Dismantled
the iMac and installed the new hard drive in it. The new hard
drive is a Western Digital 30 gig.
 
Initially the computer would hang on restart. I tried resetting the
Cuda, holding down the C key with the original iMac install CD in
the slot, tried starting with extensions off, tried to startup with
my original OS 9 system disk. Still hangs. Changed all manner of
jumper settings. Maybe it doesn't require any jumpers, not sure.
but the instructions refer to jumper settings.
 
Then trouble really began when, not being too techy, I noticed in
the start up disk control panel that there was an icon called
"network disk" or something like that. I highlighted the icon and
restarted the machine. Oh Boy! Now when it boots, I get a
statement that says type "startup" to continue or type
something else to shut down. I don't remember exactly. As I had
to leave on a trip, I reinstalled the original hard drive and put the
machine back together otherwise, I wouldn't remember the
sequences involved in dismantling and putting the machine back
together. It also seems there was some reference to firmware.
 
Any help would be appreciated. I'll cross post this to other lists
if there isn't any solution here.  Thank you for any help in getting
my friends iMac up and running, and bailing me out of a messy
situation with egg on my face. :-)

Blaine