Hi pep's. You say the O/S is pre-loaded on your machine. Have you got a CD or floppy to access the hidden partition on your hard drive and allow you to restore to factory condition or repair the existing install?
Is the PC from one of the larger suppliers or built by a local shop? If the former then there should be a restore or recovery disk, if the latter then maybe the O/S was installed for you but should have the full XP Home CD supplied with it. Can you please confirm which of the above. j.