No Hard Disk Found

When i turned on my laptop this morning, It showed a message saying ” operating system not found”. My laptop is an IBM Thinkpad T43. I then restarted the computer and went into the BIOS setup to check whether the hard disk is being seen. It is not being detected. I then tried to run a repair using a windows XP CD and the message I got was “No hard disk found, so cannot load OS….” I then removed the hard disk and connected to my desktop as an external hdd. The hard disk is being detected on my desktop and all my data is there. I can even access the data and make changes, so I don’t think its a hard disk problem

Can someone out there PLEASE offer assistance on how I can go about solving this problem. I AM REALLY DESPARATE!