Very sad car

[Toast]

So I decided tohave a weekend away in the lake district, my little pug was doing really well and hadnt had any problems until I decided to come back. Pulling into the services I noticed a louder than usual rattle, pulling out of the services there was a pop and it sort of sounded better. Any way long story short I managed to get home and had a look.

I found this wrapped round the aux belt.



Other symptoms are that anything over 2000 revs and the battery light pops up and the power steering drops out. The aux belt has slipped over a notch. The furthest cog down at the back seems to be the problem but I have no idea what this is.

Ive tralled through my haynes but I cant find ajy details of what does what with the belt.

Any help would be greatly appreciated.