Windows xp won't boot or repair

[poorcomputerboy]

Hi I have a windows xp system I am trying to get back up for a freind. Once it starts it goes to the Windows xp screen for a second then the computer reboots. Here is some of what I have tried
- F8 won't loand with any option
- tried repair but it won't recognize the previous windows installation
- recovery console it doesn't come up with the windows installation once it loads
- attached this drive to another Windows system and tried chckdisk from command propumpt and it won't repair as it does recognize the volume 
- Drive is Seagate. Ran a short and long test and drive comes back with no errors.

Just wondering if anyone can think of another way I can try to repair this installaiton as there are years of programs on the disk

Thanks in advance. 

[soybean]

Exactly how did you test that hard drive?  Was it in the subject computer or attached to another computer for the test?  What hard drive diagnostic tool did you use to test the drive?

Did this problem start suddenly, or was the computer showing symptoms over a longer period of time before this final meltdown occurred?