[CentOS] Problem with booting/grub (?)

Earlier this evening, I had the interesting experience of shutting down
my machine (because of that lp out-of-sync problem, discussed
elsewhere), and watching it not come back up.  I admit that I changed
out one of my DVD writers for another one, but I don't understand how
that could have had any effect on this:

When I restarted the machine, it came up to the point where it normally
shows: "GRUB Loading Stage 2..."

Except, it stopped at the "GRUB" and hung - no stage 2, no disk
activity, nothing, just hung.

One of the changes I made a little while ago was to modify the boot
order of my drives.  I had been booting off of the hda drive, but now
I'm booting from the sda drive.  I went through the
"grub-install /dev/sda" back then, then fixed the grub.conf because the
disk id for the root was wrong (it was showing hd2, but in order to
boot, this had to be set to hd0 because grub couldn't find anything on
hd2 - weird, 'cuz that's where the /boot and / partitions both live, but
I digress).

I thought I'd be able to recover from this by booting from hda again,
but that didn't work.  So I put in my Live CD, booted from that and
tried to fix it via grub-install from there - no go.  Grub couldn't
find /dev/mapper/livecd-rw (which wasn't there,
although /dev/mapper/live-rw was - is that a bug in the live cd?)

Then I went to my installation DVD, booted up into linux rescue mode
(which took a few tries because I forgot to boot with linux rescue
noapic), chroot'd to the right /dev and THEN I could finally run
grub-install, and finally, the system rebooted from /dev/sda.

I'm wondering:

1) What would cause the system not to get to the "Loading stage 2" part
but be able to load GRUB?  This one is really the key - if I can
understand this, I can prevent it from happening again.

2) What's with the live CD not being able to run grub-install properly?
(It also would not install using grub - I don't recall the exact error
message, but it was something about there not being a stage 1 area on
the drive, which makes no sense because it _does_ boot from that drive).

3) Is this the only way to recover from such an error (GRUB, no stage 2,
not the lp error), or was there an easier way I missed?

My configuration is:

OS :    CentOS 5.2 (2.6.18-92.1.10 Linux kernel) x86_64 with latest
updates

Hardware:
AMD Athlon 64 x2 4200+ (2 x 2.0GHz), ECS NFORCE4M-A
4GB OCZ DDR2 800MHz (PC6400)
/dev/hda    Maxtor 160MB PATA UDMA-133
/dev/hdb    Maxtor 120MB PATA UDMA-133
/dev/sda    Seagate 300GB SATA-150/300
/dev/sdb    WD 320GB SATA-150/300
/dev/hdc    Pioneer 1810 (DVR-112D) 18x DVD+/-RW/DL
/dev/hdd    Pioneer 1810 (DVR-112D) 18x DVD+/-RW/DL
 
Thanks.

mhr

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