Can I reload XP or format hard-disk using DOS-MODE ? How ?

Answer 1

No and yes.
To format a disc under DOS, you need a boot disc (1.44MB floppy) with the format program on it. You should also have FDISK on it in case you need to repartition the disk.
To reload XP you need the CD with XP and start the computer with that. Strictly speaking that is not a reload, it's an install.

Answer 2

If you want to format the disc in dos mode you need to get a floppy disc with "doctor dos" installed and use your Windows XP disc to create an emergency boot disc from the doctor dos disc. put the boot floppy into the drive and restart the computer. at the dos prompt type "format c:" (without quotes). This will completely erase all the data on your hard drive and reformat the disc (so you should have backed up any files you want to keep on a dvd-rom or second hard drive). After the format is done you will need to set the cd-rom drive as the first boot device, insert the Windows XP disc and restart. The Windows disc will guide you through the installation from here. Good luck.

Answer 3

with xp you can install only the os with no changes in other files or install with format, if you have a xp disc just put the disc in the dc or dvd drive and restart and follow the instructions, if you have a recovery disc that installations depends in how that company do the recovery disc.