mounting an external HD in 10.5.8

I am having trouble with an external Lacie 1tb hard drive. I was using it to backup my internal hd. It originally was set up by the local dealer of Mac's. The hd started malfunctioning and at 1st I thought that it was the external HD. So I tried using my external WD 2tb hd and had trouble with getting it setup. Now my system won't even recognize the external HD and tells me it can't mount the HD. Can anybody explain to me how I get the HD to mount? I have a G5 pre intel computer

If you've tried several different USB ports and the drive still will not mount, it could be defective. LaCie does not manufacture their own drives, they use drives from various other sources - WD, Seagate, etc. However, the drive itself my be OK but the electronics (drive carrier) might be defective. If the drive is no longer in warranty, you can try removing it from the LaCie carrier and place it an another carrier to see if you can get it working.