How to speed up my hard disk performance?...

You'll only see much benefit from defragment if the disk is more than about 60% full. It's much more likely that background programs are using up RAM and therefore not giving Word and other programs enough working space to open documents and edit them (depending on the size of the document, of course). You should look at what programs are loading on start-up and running in the background. Some, of course, are essential but others may be optional or even completely unnecessary. Every computer and user is different, so you have to know what each background process is doing, why it is there and whether you really need it. Another thing to investigate is whether it's worth your while upgrading the RAM. That depends on how much RAM you have, how much your motherboard is able to support and how much it would cost you to upgrade to the maximum supported.

Defrag, clear cookies and if that does not help seek professional advice.