crashed

if you can't even start in safe mode then windows is in a realy bad way.
try booting up fron a windows cd to repair it

Try putting a bootable xp disc in and try to repair your system if you remember you administration password. lol, I got this about 5 months ago and I forgot my pass so i had to format my PC, I am not sying format your PC yet some other members might have a better idea and give you better advice. But there is nothing wrong with trying this though.

Yeah it does sound like a windows problem. When a HDD goes it usually clicks and you wont see anything on screen? You can disconnect the HDD and still check your Mobo bios though?

have u sorted this m8 , have u tried using the recovery console on the windows xp disc , Read this m8 might help sort ur problem out

It is possible you have either lost or corrupted the Master Boot Record or even a virus may have corrupted it, basically that is what tell the bios which part of the hard drive that the operating system is on etc etc.
You can repair it in the recovery console though.

Hi it could be a hard drive problem I have had this in the past, if the hard drive cannot access the part of the drive where the os is then it will reboot after a few try’s which you can tell if it is doing this by listening for a ticking sound just before it reboots, it is quite a distinct sound as the drive is going over and over trying to read the sector on the drive. Best trough it and get another hdu and reload software.