Have you reinstalled Windows after formatting , if not try that and also try windows from a different source.Some times the problem can be due to some hardware like modem or multimedia card(but very rare)
so try and best of luck
Use Fdisk facility provided by many manufacturers .Also I have my doubts if both the systems you mentioned can be operated on one partition of the hard drive. On the other hand Window XP will work perefectly with other forms of Windows
Best of Luck