|Then what are you trying to boot? Does your harddrive contain a pre-existing operating system? If so the that is your problem.|
An operating system (Particularly XP) that was installed in one hardware environment will not boot up when transplanted into a new system.
If you wish to keep that old installation and it's files etc then you will need to do a repair install. Set boot order in BIOS to CD first and insert your XP CD. Restart and when setup asks the first question about whether you wish to install or enter repair console. choose install. It should then detect your existing operating system and ask if you wish to repair or do a fresh install. At this point choose "R" for repair.
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