It then tries again etc,at one point it gave a CPU temperature warning,now it gets to the beep of Vista then gets in trying to start/turning off loop,help.

Could be a number of things, software (system error or malware) or hardware.

For a start:
Have you tried f8 and into safe mode?
Have you got another computer to burn a disc to?
If so it might be worth burning a boot cd to run some tests.
http://www.hiren.info/pages/bootcd
Have you cleaned the inside of the PC out at all?
How old is the PC?

If you can get into windows try a program called OCCT, its a program that allows you to stress test your PC's CPU or GPU. It also reports the temps while its testing, its a good way to see if anything is overheating.

It sounds (and this is guesswork) as if it became too hot and kept shutting itself down to protect the CPU, and this has caused errors on the registry.

Clean the CPU and put new thermal paste on it, then use your Windows disc to run a registery repair (or run ChkDsk) and this should clear any minor errors.

Hope this helps.

Check the heat sink on top of your CPU .. "look for a broken clip" .. it may have come away i`ve had this before on older AMD heat sinks

Thermal Event.
The computer is being shut down to prevent damage.

Loose heat sink.
Dried thermal paste.

Check the bios settings incase the temperature warnings are too low.

Thanks,I found that 2 of the 4 clips on the heatsink were loose,pushed them back in,they clicked and now my PC is working again,thanks to everyone for their help.

Your welcome mate,Its always nice when people come back with an update