I have had a stoke of luck with the whole failing to boot issue.
Following on from what Rick had said about the problem being potentially
with the graphics card, I went to update the graphics card driver,
(previously listed as the most up to date version) and a new one was
available on Nvidia's website. (The graphics card i have is an ASUS
EN8800GT) I have installed the new driver and i am not getting the
restarts during the boot up like before. The date for the driver on the
website is 20/12/2007, so if you are running one from before this, it is
definatly worth downloading.
If your still having problems with vista booting, i recommend getting
the new driver update from the website.
'Drivers - Download NVIDIA Drivers'
(
http://www.nvidia.com/Download/index.aspx?lang=en-us)
Upon updating the driver, i found that the original driver that came
with the card was infact for a 32-bit system, so if you are running x64,
you should find that this helps.
Do not use the device manager to look for an updated driver, the one
that it found caused my computer to continually fail the boot, (8 failed
starts in succession) and I had to restore back to my last known good
configuration to allow me to boot it back up.
I hope that this maybe of some help to people in sorting out what is a
really annoying problem.
--
clarkeboy