If the mechanism is the same (or similar) as the S4, then it can get clogged up with sh1te which eventually seizes it up. If it hasn't failed completely, then the solution is to remove it and give it a good clean. A bit fiddly but not difficult.
I'll have a look at mine tomorrow and if it's the same or similar, I'll post up the 'how to'.
As for the ESP light, that's a bit of a mystery unless you've simply dislodged a fuse.
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Present: S4 B8 avant, fully loaded, MRC Stage2, Milltek non-res, KW springs
Past: S8 D2 FL, S2 ABY coupe, RS6 C5 saloon, RS4 B7 saloon, S4 B5 saloon, S4 B6 avant, all gone but not forgotten 
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