Sony Vaio, Win XP will not load completely. Machine will continually restart

I have had a Sony Vaio Desktop for three years now and have just recently had problems. Currently my problem is Win XP will not load completely.

Here is what happens---

When I start the machine it loads normally at first.
Then I get a screen asking me if I want to boot in safe mode, last known good configuration, etc

I have experimented with all the options available and get the same result
After I choose a boot method, (i.e. safe mode, etc) I will see the Windows XP logo with the green meter running below it, then a blank screen after that for about 15 seconds.

After that, the machine will automatically restart and will continue to do this until I shut it off.

I have been hesitant in using the recovery wizard (F10) because I am not backed up. I would like to get get back to normal so I can get backed up

Any ideas?
Need further info?

John