computer freezes in windows xp black screen

When I'm starting up my hp pavilion 471.uk, it freezes on the black screen saying windows xp with the blue squares moving at the bottom. It just sticks on it!
I tried to attept a system recovery but it stuck on the hp screen with the blue square moving at the bottom. Whatever I press I can't get out of it so the only way is to pull the plug on it and after several attempts it will get past this screen.

Any ideas what is wrong please?!

Be careful how you close down your PC. It might knacker your Hard drive by just disconnecting the power. Acceptable shut-off is to hold in the PC's power button for a few seconds then it should power off as in an emergency. This, also, should be used infrequentluy if at all.
Try tapping F8 (F5 on some PC's) to boot up to a screen that offers a choice of startup procedures. Use the arrows keys on your keyboard to select 'last known good configuration'.
Don't panic after tapping F8 on startup if you get a long list of strings as it will then go to the selection screen.