Most of the computer systems come up with either a recovery CD/DVD or a recovery partition that is hidden on the computer. This is true for most HP and Dell machines now these days.
If you have any one of them then you can try the recovery from windows or during the startup.
If yo have HP then go to start, all programs, hp tools and then select HP PC system recover.
hp recovery manager
you can also press the F10 key multiple times during boot-up to get access to the recovery console in case windows is not loading properly.
If you have dell then you can access the recovery partition by pressing the ctrl + f11 immediately after the machine is turned on.
PS: All of you data will be lost on the hard drive. using the recovery cd is not the same as repairing cp. when you repair windows xp, all of the system files are replaced with the original ones, but your data and applications remain intact.
I think this might sort out your issues, if still something is not right then contact to these people. They will guide step by step with another mechanism.