Power Macintosh G4 Won’t Boot After Plugging in External HDD – How to Fix

Last weekend I got an old PowerMac G4 "Gigabit Ethernet" and it worked fine for a few hours. Then after plugging in my external HDD to copy some of the data over, the system went to sleep and wouldn't turn back on. I proceeded to turn off the Mac and unplug the HDD; once I rebooted, I was met with a long load time (about two minutes) with no Apple on the light-gray screen — followed by the Finder icon with a question mark.

I looked up articles and forums to help, but so far nothing has worked. I have tried pressing Alt+R (Command+R) to get into the recovery menu — and while the menu does appear just fine, there's no option for anything to boot from; it just shows me the "reload" icon and an arrow pointing to the right.

Another thing I tried doing was I burned an .iso of Mac OS X Tiger (the Power Mac has 10.4.11) and try loading that from Recovery mode, but it still does nothing; the disc doesn't appear in the menu. In fact, the disc barely spins in the drive; the LED just blinks a few times when the system powers on, then quickly stops trying to read the disc.

The only thing I can think to do now is go into OpenFirmware (I do this by pressing one of the buttons below Power), but I haven't found a solution that works here. I might try booting from the CD, but if the CD didn't show up in the Recovery mode, I doubt it would show up in OpenFirmware.

While in OpenFirmware, I went and entered a few commands, as advised by @Allan. Here is the output from devalias:

pci0              /pci@f0000000
agp               /pci@f0000000
pci1              /pci@f2000000
pci2              /pci@f4000000
pci               /pci@f2000000
fwx               /pci@f2000000/firewire@12
enetx             /pci@f2000000/ethernet@13
enet1             /pci@f2000000/ethernet
fw1               /pci@f2000000/firewire
cb                /pci@f2000000/cardbus@1a
cbx               /pci@f2000000/cardbus@1a/pci-bridge/pci-bridge
usb0              /pci@f2000000/usb@18
usb1              /pci@f2000000/usb@19
mac-io            /pci@f2000000/mac-io@17
mpic              /pci@f2000000/mac-io@17/interrupt-controller
ide0              /pci@f2000000/mac-io@17/ata-3@20000/disk@0
ide1              /pci@f2000000/mac-io@17/ata-3@20000/disk@1
hd                /pci@f2000000/mac-io@17/ata-4@1f000/disk@0
cd                /pci@f2000000/mac-io@17/ata-3@20000/disk@0
zip               /pci@f2000000/mac-io@17/ata-3@20000/disk@1
ultra0            /pci@f2000000/mac-io@17/ata-4@1f000/disk@0
ultra1            /pci@f2000000/mac-io@17/ata-4@1f000/disk@1
scca              /pci@f2000000/mac-io@17/escc/ch-a
sccb              /pci@f2000000/mac-io@17/escc/ch-b
ki2c              /pci@f2000000/mac-io@17/i2c
ki2c-serial       /pci@f2000000/mac-io@17/i2c/cereal
via-pmu           /pci@f2000000/mac-io@17/via-pmu
rtc               /pci@f2000000/mac-io@17/via-pmu/rtc
adb               /pci@f2000000/mac-io@17/via-pmu/adb
adb-keyboard      /pci@f2000000/mac-io@17/via-pmu/adb/keyboard
adb-mouse         /pci@f2000000/mac-io@17/via-pmu/adb/mouse
adb-eject-key     /pci@f2000000/mac-io@17/via-pmu/adb/eject-key
wireless          /pci@f2000000/nac-io@17/@30000
ui2c              /uni-n/i2c
ui2c-serial       /uni-n/i2c/cereal
enet              /pci@f4000000/ethernet
fw                /pci@f4000000/firewire
keyboard          /pseudo-hid/keyboard
mouse             /pseudo-hid/mouse
nvram             /nvram
sound             /pseudo-sound
eject-key         /pseudo-hide/object-key
last-boot         /pci@f4000000/ethernet@f
screen            /pci@f4000000/ATV ,Rage 128Pd@ 10

Entering the command printenv yielded this result:

-------------- Partition: common -------- Signature: 0x70 --------------
little-endian?          false                false
real-mode?              false                false
auto-boot?              true                 true
diag-switch?            false                false
fcode-debug?            false                false
oem-banner?             false                false
oem-logo?               false                false
use-nvramrc?            false                false
use-generic?            false                false
default-mac-address?    false                false
real-base               -1                   -1
real-size               -1                   -1
load-base               0x800000             0x800000
virt-base               -1                   -1
virt-size               -1                   -1
pci-probe-mask          -1                   -1
screen-#columns         100                  100
screen-#rows            40                   40
selftest-#megs          0                    0
boot-device             hd:,\\:tbxi          hd:,\\:tbxi
boot-file            
boot-screen          
console-screen       
diag-device             enet                 enet
diag-file               ,diags               ,diags
input-device            keyboard             keyboard
output-device           screen               screen
input-device-1          scca                 scaa
output-device-1         scca                 scaa
mouse-device            mouse                mouse
oem-banner       
oem-logo            
nvramrc             
boot-command            mac-boot             mac-boot
default-client-ip       
default-server-ip       
default-gateway-ip      
default-subnet-mask     
boot-script            
aapl,pci                Use PRINT-APPL,PCI to view
ram-size                30783430 30303030 3030

So, TL;DR – because I stuck a USB device into my PowerMac, it has forgotten where the boot sector is.

Any help would be greatly appreciated!!