Defragment

does fragmenting causes ctd 's if you have mods after you defrag your game?

It never hurts to defrag. A fragmented harddrive will slow loading of any program and it can cause ctds because the data is not being tranferred fast enough. I defrag once a week.

No, defragging will not cause a crash to desktop. Infact, defragging will improve access speeds for the files, and games which depend on reading data frequently from the drive (eg. Oblivion, MS flight sim) will benefit greatly from a defrag, especially when directories are consolidated.

Defrag regularly; it's good for the system. In fact these days there are automatic commercial defragmenters that clear up fragmentation in the background as well as prevent much of the new fragmentation, all without requiring any user action