When the splash screen appears and the icons / words appear on the bottom of the screen you need to press 5 on the qwerty sde of the keyboard between the keyboard icon / word and the speaker icon / word, before the system beeps.
The F5 key was phased out a while ago now.
Boot the system and watch the screen, just in case kep tapping F5 and 5 alternalely to fill the keyboard buffer, then the system should recognise one or the other and boot the default service mode boot list which should have the CD before any hard disks.
If you have a serial console you can hit any key whilst the system is at standby and you should see the servie processor menu.
From here / the boot sub-menu you can select the cd as the boot device or if not, boot to sms and then select the cd as the boot device.
Also from the service processor menu you should see the firmware level in the second line of the title.
For the p630 AIX 5.3 support was added at firmware level 3R040323
The last part of the level - 040323 - is a date code, 23rd March 2004, if your firmware is earlier that is probably your problem.
If you have a floppy drive you can update the firmware from the service processor menus.
Firmware update readme:
http://download.boulder.ibm.com/ibmd.../70286C4F.html
Firmware for the p630:
http://www14.software.ibm.com/webapp...1&mtm=7028-6C4