Currently Being ModeratedSep 7, 2012 12:29 PM (in response to SurMixAPrise)
See here: iPod Displays a Red "X" Icon
Note that it is often the sign of a hardware failure, usually with the iPod's hard drive. You can try slapping it again your leg with a bit of force as it may just be that the drive's read/write head is out of place.
If no luck you'll want to have your iPod serviced or replaced either by Apple or a third party repair company.