Use a better defragmenter. Norton Speed Disk has REALLY gone downhill in the past few years. For modern OS'es the only defragmenters I can recommend are:

O&O

and

PerfectDisk

Everything else is a waste of time and money. Especially avoid DiskKeeper for two very good reasons:

1. Written by freaky scientologists. Every penny spent on it helps keep Katie Holmes enslaved.

2. It is known to corrupt data in rare circumstances... but often enough that reports of it are all over the Internet.