In my previous experience, I never had problems regarding conflicting software, rather I had problems regarding registry permissions. I was able to fix it by following this guide. One advice though: turn off most programs running in background such as real-time antimalware. At least you may reduce possible problems brought by running programs because the system cannot terminate them.
what your suggests if I have problem when upgrading to SP3 ? honestly, I really worry to do this because my original XP CD is missing.
Can you get the 25 digit key?
Standard Hooplah
The Magical Jelly Bean Keyfinder is a freeware open source utility that retrieves your Product Key (cd key) used to install Windows from your registry. It allows you to print or save your keys for safekeeping. It works on Windows 95, 98, ME, 2000, XP, Vista, Server 2003, Server 2008, Office XP, Office 2003, and Office 2007 family of products. It also has a community-updated configuration file that retrieves product keys for many other applications. Another feature is the ability to retrieve product keys from unbootable Windows installations.