Well, I still wasn't able to fix this darn problem without reinstalling win xp. I came across these two little utilities:
ERUNT and NTREGOPT. They are utilities to back up and defragment your registry. I tried them, but it crashed win xp and even prevented it from booting (i had to use recovery console to get back on track) so i suggest using it only if you know what you're doing. If anybody actually manages to fix it with these utilites, let us know. Still finding an answer to this one, phew...