One or more disk are failing?
 

i installed fedora 11 linux in my computer.but after successfull installation,i see that a message near the taskbar that "A hard is failing". what is that suppose to mean?????

This is a message from Palimpsest, a desktop application that monitor the state of the disks with S.M.A.R.T. capabilities. Googlin' around, you can see that this issue has been reported many times as a false positive. However, better to check the disk(s) using fdisk (be careful if you're not experienced) or using the utilities from the disk manufacturer (if available). In any case, it is always strongly advised to keep a backup copy of your valuable data.