try this . go to ur bios setup ask to run cd rom drive on boot
as first priority.
put in ur xp/vista cdrom
click install windows XP
On the setup screen use the second option which indicates you
should repair the Windows installation by pressing the ‘R’ key
On the following page you will need to select the drive that has
Windows XP installed on it. Most probably you have Windows
installed on the C drive. If you only have one partition or one
drive you will see the DOS screen; otherwise you might have more
than one drive option to choose from.
If you have selected the C drive as your partition that contains
the windows installation you should see a command prompt that is
defaulted to C:\Windows>
At this command prompt type "chkdsk/f" withoth the quotes. Then
hit enter to check your disk WITH FIX. This will check only the
drive that you selected. If you have more than one drive this
will check only the drive that has Windows.