How do you know if wine has gone bad? Which smells indicate that wine/beer is bad?and can it have any negative effect on health?
Here is a list from the Wine Faults Wikipedia page. These faults, for the most part, will not do any harm when they are in wine (they aren't strong enough) They just taste bad.

Acetaldehyde    Smell of roasted nuts or dried out straw. Commonly associated with Sherries where these aromas are considered acceptable

Amyl-acetate    Smell of "fake" candy banana flavoring

Brettanomyces   Smell of barnyards, fecal and gamey horse aromas Cork taint Smell of a damp basement, wet cardboard or newspapers and mushrooms

Butyric acid    Smell of rancid butter 

Ethyl acetate Smell of vinegar, paint thinner and nail polish remover

Hydrogen sulfide    Smell of rotten eggs or garlic that has gone bad

Iodine  Smell of moldy grapes 

Lactic acid bacteria    Smell of sauerkraut 

Mercaptans  Smell of burnt garlic or onion 

Oxidation   Smell of cooked fruit and walnuts. Also detectable visually by premature
    browning or yellowing of the wine 

Sorbic acid plus lactic acid bacteria   Smell of crushed geranium leaves 

Sulfur dioxide  Smell of burnt matches. Can also come across as a pricking sensation in the nose.