Please I Need Help With My External Hard Disk Drive

I have this rather strange problem with my external hard disk drive. it works on my laptop and any other desktop and laptop as well but it just wont work on my desktop. at first I suspected the USB port but I tried the port with another external hard drive and with a flash drive, it worked perfectly fine. my desktop is a pentium 4 mercury board computer and just in case you're wondering I have also tried this particular external hard drive on a mercury board pentium 4, it worked but it just work on mine!!!
Im thinking of reformatting the computer but I just wonna be sure if that's the best shot besides I wonna copy the drivers in the system out before formatting as I don't have any other drivers to install after formatting. please anyone with a better idea should help.