Does defragmenting in Windows.....

kill your datas? or crush your PC? I do defragment sometimes but I'm so scared each time I do it. So please tell me the answer. Because my external hard drive is being quite slower then usual nowadays, I think I have to defragment the ex hard drive. Or is there anyother solution??

Defragmentation is INCREDIBLY DANGEROUS YOU SHOULD NEVER DO IT.

Just kidding.  You should probably defragment your hard drive (if you run Windows) every few months.

As a correction to >>2, NTFS still needs to be defragmented every once in a while, just like FAT filesystems.  ReiserFS uses a dancing trees algorithm AFAIK, so it "defragments" as you add, relocate and remove files.