Windows XP is Running Extremely Slow

I bought my computer on march 2005. It runs a Windows XP with 2GB RAM and 150GB HDD, Pentium Processor 1.7GHz. My problem is, whenever I try to click any icon on my desktop, it will take time before it opens.
I already run Kaspersky to scan for any virus but it is still the same.
I also run a defragmentation and nothing changed so far.
I do not have much on my computer but I really don't know why its acting very slow.
Can someone please help me?
