Things that happen "sometimes" are difficult to diagnose as they are often related to hardware issues.
I'd start with making a new account (if XP loads succesfully) and login to that. Might just be better. If not, it's time for a clean install (back to factory conditions) of Windows from your XP or recovery CD.
I have this problem since few weeks.
When i start my pc, when windows xp starts to load sometimes there appears a black screen, nothing else.
But sometimes win xp loads succesfuly and after I logon there appears again black screen.
I tried finding a fix for it in google but nothing helped, it`s getting me angry.
It sucks can anybody help about that I will appreciate. Thanks!!!