My laptop (2.6GHz Celeron, 1Gb RAM, 80Gb HD, Windows XP Home SP2, 56k dial-up modem) has been slowing down badly over recent months, particularly when online, and I've mostly attributed it to Norton's heavy use of system resources (Internet Security 2006, and kept up-to-date) or to incoming updates for Norton or Windows, but I have noticed on occasions that svchost.exe has been using a lot of CPU.

This may be unrelated, but in recent times, I've had very frequent disconnections while online for browsing, downloads or e-mail, and lately, initial connection to the ISP server has become unreliable, often requiring several attempts. My ISP says it's not a problem at their end. There is nothing in my dialler / internet / mail settings that appears incorrect or has changed. I deleted the internet connection and created a new one, and re-entered my internet account password everywhere it's required, just in case, but nothing changed.

Now however, things have gone drastically amiss, CPU usage is up to 97%-100% much of the time with no good reason, programs are naturally incredibly slow to start or operate, and the System Processes list shows that Winlogon.exe and/or Explorer.exe are hogging the CPU resources.

Norton can't find a virus, even using Symantec's over-the-web scan, and Ad-Aware and Spybot S&D detect no spyware or trojans etc. I've run Norton Utilities WinDoctor and PCTools Registry Mechanic 5 which both found problems and fixed them, which improved matters a bit but the computer is still inclined to suddenly go into 100% CPU usage and become almost unusable.

I've 'Googled' for solutions to similar CPU-hogging problems but haven't been able to decide whether what's wrong with my machine is exactly the same as the problems described by others.

Any ideas would be greatly appreciated.

Thanks !