Hitting Shift-PgUp when I first get to the emergency mode screen does absolutely nothing. Hitting Shift-PgUp after logging in as root to get into maintenance mode does nothing there either.
Some additional information: With the SCSI adapter card installed, during the bootup process, before the screen where you select which vintage of Centos you want to run, a message appears showing the Adaptec AHA 2930CU and mentioning a BIOS version. I did a search to see if there was a more recent BIOS version available. Apparently it is not flashable on that particular card. However I did come across a procedure for entering the Adaptec BIOS by pressing control-A while the message is displayed. I also learned that the Adaptec BIOS essentially hijacks the boot up procedure, which would make sense if the operating system was on a SCSI hard drive attached to that controller. There is an option in the Adaptec BIOS for disabling it if that is not the case. I subsequently went in and disabled essentially all the options there. I then powered down the server, cleared the motherboard CMOS, and brought it all back up. I was really hopeful the problem was fixed, but no joy. I guess I should not have been surprised in view of the fact that pulling the card from the system didn't reverse the problem either.