New SN85G4, New problems

Having recently conquered my missus' new SN85G4 problems, my first ever
shuttle, I decided that having used her as a guinea pig, and not to be
outdone, I would follow suit with a brand new shiny small computer. Firstly
I will list what went in it, then divulge the problem
SN85G4 w/standard PSU
512mb 3200 unregistered Corsair platinum memory
AMD 64 Bit 3000 cpu
Sony DVD/CDRW
Leadtek winfast 5900XT video card
Western Digital 120 gig SATA drive
win XP home

Having previously built one of these things, I thought this would be easy, I
jury rigged a floppy drive in for the install, and got windows to start its
setup properly, it rebooted, dutifully continued till it got the installing
devices bit, then stopped dead. I clicked on the screen after waiting a few
minutes and it rebooted itself, and continued from the previous step, It got
a bit further this time then blue screened, I rebooted and the post screen
for the gfx card came up and got stuck, rebooted and the post screen for
the gfx card came up again, got stuck and half of it was gibberish. I
switched off, went for a moan at the missus, came back and switched on, the
computer continued loading windows. It managed to finish the install, had to
be rebooted, was fine, installed some board utilities, had to reboot, and
the post screen for the gfx card didn't even show, the whole thing just
flickered crazily like a spectrum loading screen till I switched it off.
I rebooted and all it said was "bios checksum error checking for drive A:
media. no Drive A found, system stopped."
So, I panicked horribly, went to tell the missus, came back and switched on,
hey ho, it worked, managed another reboot, got stuck on the GFX post screen
on the next. If it runs for any period of time, it will eventually freeze,
drop and get stuck posting.

My missus' shuttle is exactly the same as mine, save that her HDD is a
Samsung 80 gig SATA, which I have noted, is smaller than the Western Digital
one I put in mine, which sticks an extra inch out of the back of the caddy,
I am tempted to blame this.
I think something somewhere is overheating, the PSU does seem to get a
little warm, At first I was blaming the GFX card and the rough handling the
courier gave it, but I,ve noted that its not getting hot itself at all, so I
don't think thats it. I used Arctic aluminum paste for the CPU die, which is
the only other difference between my machine and hers. Could the extra
length of the HDD cause cooling problems with airflow or something? Given
the ease with which the components in these things go together, I find it
more than a little upsetting that getting them to actually work seems to be
a different issue.

Regards,
Motoko
--
"Life is a disease, sexually transmitted and invariably fatal"
Death - Insert on HIV in Vertigo comics sometime in 1996