XP SP3 Windows Explorer (Not IE) Freezing

I am able to use Explorer OK in safe mode for looking at folders and files but not in normal mode. My PC boots OK and quickly, but takes ages to display the taskbar. It sits just showing the desktop for 20 minutes + I am able to load task manager and can run my browser through task manager OK. When it eventually allows access to the Start menu it will freeze again as I run the mouse over the menu options.