I have recently bought a punto gt, spent ages looking for one. When i test drove it all was fine, but the day after i got it the ABS light came on and has been on ever since. The brake pedal is low, I was thinking of bleeding the brakes and seeing if that would help, any ideas?

Check the ABS sensor on the wheels, check to make sure the pads arn't worn down, replace the brake fluid and disconnect the battery for 15 mins.
Should sort it.

I have fully bled all the brakes and disconnected the battery for an hour, when i put it back on a siren started and wouldn't stop [}] in the end i had to take it apart and cut the wire to it. ABS light still on. I have looked at the sensors but i don't really know what i'm looking for!

The best thing to do is disconnect the abs plug by the engine and spray it with carb cleaner, that will solve your problem.