It sounds very much like 'something' has stopped responding. Try doing Ctrl+Alt+Del and you will get something call the Task Manager which may show you which componet has. Just end task it and then reboot the laptop.
If you can't get that far then you may need to turn the laptop off and then back on again. In some cases you have to resort to removing the power and the battery to force it to die.
This is very rare in XP but it does sometimes happen!