Lockup playing AVI file with pivoted display

My 2002-vintage computer has a recently-installed CPU and LCD display.
The computer locks up with the display pivoted 90 degrees via
irotate.exe while playing AVI files using Nero ShowTime, producing a
medium-high-pitched sound. The lockup seems to happen only when the
display is pivoted. Nero ShowTime is the only program I have which
will show AVI movies while the display is pivoted.

The last time this happened, CPU temperature was 43 degrees C and CPU
utilization was about 30 percent.

I reset the computer to recover from these lockups, only to find that
CPU hyper-threading is disabled until I restart Windows, which runs
very slowly, and then restart the computer and Windows again.

Does anyone have suggestions about how to stop this lockup while the
display is pivoted?

System description
Windows 32-bit XP SP3, Nero 6.6 including ShowTime 2.0.1.9,
irotate.exe 1.37, Microsoft Security Essentials, 2010 Tune-up
Utilities. Dell 2700FP LCD monitor A02, 1600x1200 pixels (pivoted to
1200x1600), 32-bit color, DVI cable. Gigabyte GA-8IEXP motherboard
(533MHz FSB), 1.5GB PC-2700 ECC memory. 3.06GHz Pentium 4 CPU
(Northwood with hyper-threading). Radeon 9000 AGP-4X video board.
Samsung 200GB and 250GB IDE internal drives, Samsung 1.5TB eSATA
external drive, SiI 3512 eSATA controller board, 6Mbps DSL via 2-Wire
AT&T 2701HG-B gateway.