If you have an XP CDROM, try running the recovery console form it. This is
a DOS-like envirnornment, in which you can fix some things. For example,
run CHKDSK C: /R.
If you do not have an XP CDROM, you can download the equivalent of the
recovery console form Microsoft. They call it installation floppies. You
download an image an it makes several floppies for you. Be sure to label
the floppies in the order made.
If none of the other suggestions you have receive work, then consider doing
a "repair" installation of XP. A "repair" does not format the hard drive,
the way a full installation does.
However, a "repair" can only be done with a retail version of XP. If you
have an OEM version (e.g., from ell, Gateway, etc), this option is probably
not availble.
Caution: Many OEM PC makers provide a "restoration" CD. Do not use that,
unless you are willing to lose everything on the hard drive.
An alternative to a "reapir" is a parallel installation of XP, esentially a
second XP on the same PC. However, this requires a spare aprtition, and
most PCs does not have that. Of course, if this is a desktop PC, you could
add a second hard drive, and then install a second XP on that. Anyway, the
second XP can be used to fix the first XP, or recover files.
It may be possible to recover files from the hard drive, independent of
fixing XP. There are several LINUX-based rescue CDs that are free on the
web. You download their image, then burn to CD, then boot PC from the CD.
I like KNOPPIX, but that is a very large download, about 700 Meg.
It may also be possible to recover files via an old-fashioned DOS boot
floppy, or floppy image made into a bootable CD. If the hard drive is
formatted as FAT32, this will work directly. If it is NTFS (likely under
XP), DOS can not see it. But, there are free DOS drivers for NTFS that
allow you to read/copy from NTFS to somewhere else. These are available
from
www.sysinternals.com. If you need a DOS (win 98, really) boot disk, go
to
www.bootdisk.com.
Finally, consider making a Bart's PE Builder rescue CD. If better than the
recovery console, and better than a DOS floppy.
http://www.nu2.nu/pebuilder/index.php?p=1