Power steering not working

[Brods]

Hi looking for some help.my power steering has stopped working. And the warning light has come on in the dash ( steering wheel and exclamation mark in red. ) any ideas the problem. Thanks 

[Greenmamba]

Have you checked that the power steering belt is on?

[Brods]

Yes it's still on

[Greenmamba]

How's the power steering fluid level in the reservoir and are there any bubbles in it when the motors running?