PC Keeps rebooting when loading up XP

I'm not sure whether this should be in the software or the hardware forum as I think it could be either. Anyway my housemate asked me to add a hard drive he had that contained a load of files he wanted. I connected it up and the BIOS recognised the extra hard drive in the configure of master and slave but it would freeze up XP. I decided that it wasn't going to work and so set everything back up the way it was before (Connections, jumpers etc) but now it would lock up before it got to loading up XP. I put in the XP disk and ran chkdsk and this managed to reboot the pc and XP. I restarted XP to see if it was working fine and it started up again with no problems.

However now my housemate has now come up saying the pc isn't working. All that happens now is that it loads up and then says if you would like to start up in Safe Mode etc etc, whatever you pick it just reboots the pc straight afterwards. I've even tried with the XP disk and it starts to run the XP Setup but again the pc just reboots before any options come up (I have noticed that while XP Setup is running through various things i.e keyboard, mouse etc just after it's running a FAT32 I think it was it reboots everytime.

As far as hardware is concerned, I can see that the fans are all running, the hard drive is being recognised in the BIOS, I haven't changed anything in the BIOS.

Could it be cables aren't connected properly somewhere? Is the hard drive on it's last legs?

Any help you can give I will grateful, thanking you in advance.

P.S Sorry for the lack of technical specs but I didn't build the machine.

 

Cheers but still not working, have tried another hard drive the hope to do a complete reinstall but still when it's booting up from the XP disk it gets to what I can see loading FAT and then Windows NT it reboots.