Didn't notice the part about needing an expert.  Sorry.

What is your operating system?

WIN98

XP

VISTA

Windows 7

If one of the last 2 they defrag automatically in the background.  However I and most on here are going to doubt your slow down has anything to do with defraging.

You probably have some virus or trojan.  Go to http://download.cnet.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?part=dl-10804572&subj=dl&tag=button

Download the file to your desktop.  (the screen that you see all the time with all the icons) then after it's downloaded double click with your left mouse button and follow the instructions.  Once installed you will click on update to get the latest data and then click on scan and choose "FULL SCAN"  It might run for an hour or more.  At the end you click on "SHOW RESULTS"  and then in the next window click on "REMOVE SELECTED."