[susan53]

1A : it's a compound noun with the first noun acting adjectivally - and adjectives are never plural in English. Another example - a horse race. You'd never say a horses race.

But 2B : as the subject it would be the main noun. Computer can't be used uncountably (as for example science as in I have science this afternoon) and so would have to be plural -though I can't for the life of me think of another example. Academic subjects are nearly always uncountable.

Actually, though, would you say it at all? It sounds odd to me. I'd say I have ICT(Information and Communications Technology)