windows xp in continuous restart loop.

you need to repair using disk or preloaded os

have tried using disk and recovery console:  fixboot, fixmbr.  Did not repair

did you try to fix with repair wizard?

disconnect any usb drives until it boots then reconnect

remove disk from cd tray and reboot :)

It sounds like your system is going to the bsod, and automatically rebooting. If the system will not even boot to safemode, it looks like your operating system is toast. You may need to back up your data then reinstall the os, and applications. Otherwise you can waste hours trying to repair the operating system, and still find that the operating system is not stable. If you have external media to back up the computer you can create bootable media on another computer such as the ultimate boot disc, then access your data from the corrupted drive, and back it up on your external media such as memory sticks, external hard drives, optical discs (DVDs or cds), etc.  Once the data is backed up wipe the drive and then reinstall windows with your windows discs. If this computer is a HP or Dell or some other large manufacturer, there may be a recovery partition on the drive that will recover your computer to a state when you first purchased the computer. Mind you, you will still need to reinstall any apps that you installed on your system since you have first got the system. You will also lose your data. That's why you need to back up first.

may i ask what you have on screen when it reboots?  up to where does it get?
i suggest to run a ram and disk diag first -  before trying ANY repairs  - to be sure about the basics.
it can be the OS - but also bad ram or disk (or other parts)
i use for diags the UBCD :
Hardware diagnostic CD    UBCD

go to the download page, scroll down to the mirror section, and  click on a mirror to start the download
Download the UBCD and make the cd   <<==on a WORKING PC, and boot the problem PC from it
Here 2 links, one to the general site, and a direct link to the download

since the downloaded file is an ISO file, eg ubcd527.iso - so you need to use an ISO burning tool
if you don't have that software, install cdburnerXP : http://cdburnerxp.se/

If you want also the Ram tested - run memtest86+ at least 1 full pass,  - you should have NO errors!
 
For disk Diagnostics run the disk diag for your disk brand (eg seagate diag for seagate drive)  from the HDD section -  long or advanced diag !  (runs at least for30 minutes)

http://www.ultimatebootcd.com/                        ultimate boot cd
http://www.ultimatebootcd.com/download.html             download page

IMHO the most time saving way and easiest way is

firstly, try to recover with cd with wizard window.
if fail then backup your file and then do a clean installation.

after you done everything i suggest you to clone your window and backup your file often to prevent this incident happen again in the future.

another solution can be this :
http://support.microsoft.com/kb/307545
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An easier way is to boot from a Bart PE CD (or UBCD4Win CD) and use the file manager for manipulating files. Here  the procedure :
1. rename c:\windows\system32\config\SYSTEM to c:\windows\system32\config\SYSTEM.bak
2. Navigate to the System Volume Information folder.
it contains some restore {GUID} folders such as "_restore{87BD3667-3246-476B-923F-F86E30B3E7F8}".
The restore points are in  folders starting with "RPx under this folder.
3. In such a folder, locate a Snapshot subfolder. This is an example of a folder path to the Snapshot folder:  C:\System Volume Information\_restore{D86480E3-73EF-47BC-A0EB-A81BE6EE3ED8}\RP1\Snapshot
4. From the Snapshot folder, copy the following file to the c:\windows\system32\config folder
 _REGISTRY_MACHINE_SYSTEM
5. Rename _REGISTRY_MACHINE_SYSTEM to SYSTEM
6. Exit Bart PE, reboot and test

Use a fairly recent restore point from at least a day or two prior to problem occurring .

** you can add the other hives also with this procedure

http://www.nu2.nu/pebuilder/       BARTPE
http://www.ubcd4win.com/            UBCD4WIN

Using the safe boot menu (pressing F8 as it is booting), select boot to command prompt. Are you able to get to a  command prompt?

no command prompt.  Disabled restart and got blue screen:

unmountable_boot_volume

do NOT run chkdsk - first ensure the disk runs ok with a disk diag, as i posted above

I would definitely consider hardware failure, such as a bad hard drive, As I first mentioned the system is mostlikely going to the bsod. Now that we know that the BSOD is showing an unmountable boot volume, this is saying that there is either a hard drive that is failing or your system's operating system is corrupted to a point you most likely will need to use a boot disc such as the ultimate boot disc as mentioned by myself and other commenters. You can use the boot disc to boot to an environment to both test the hard drive or to recover your data, to let you back up your data. Then do a clean install. If the hard drive is failing it is important to backup your data asap before it fails completely and you loose all access to your data. If you wait until you get to that point, you will have to pay mega bucks to recover your data, if they can recover it all.

how is it going ycguy ?  any comments?

yc guy - what was the solution?