Windows XP Pro Freezes/Lockup

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PC came in, boots up to desktop, and periodically freezes. Could be
within 1 minute of bootup, could be 5 hours. Ive switched the ram into
all 3 slots, switched out power supplys, and switched the processors,
even fan/heatsinks. Ive tried a reinstall of XP - it freezes during
installation, any ideas?

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