I have an assembled PC that is about six years old. It has an Intel Pentium 4 2.4 GHz based CPU. I run Windows 2000 XP Home Edition as the operating system software. The computer has 1 GB of RAM installed in it. Lately the computer seems to have slowed down a lot. The hard disk light is constantly on showing activity whether any software is working or not. I have AVG antivirus installed on the computer with a firewall. I have tried cleaning up the hard disks and defragmenting them also. Nothing seems to work. What could be the possible issues to address?