Thanks for all the advice so far about other problems.
This time my computer tends to reboot at random when I click on something or open something. This is weird because it reboots only some of the time, not always. For example it sometimes reboots when clicking on a file to download when using LimeWire, sometimes reboots when opening Internet explorer, and sometimes reboots when doing a Windows Search, or sometimes when running a scan with a virus/adware checker.
I read the post posted by ndion35 and checked the event manager on MyComputer, and found red X's around the time of last reboot. The file source is "nview_info".
Also a new problem I have is when windows XP restarts, it shows a error message that reads: "Error: Event Logger not found" . The screen remains clean with just the windows wallpaper and no desktop icons or taskbar (cannot access taskbar or start menu). I opened the task manager with alt+ctrl+del and launched explorer, and all the desktop icons and taskbar appeared and windows works as normal. But I have to do this every time the computer reboots. This new problem arised after I had the Trojan smitfraud virus. The computer had the reboot problem before this though
Thanks, hope you have some advice!