I too cant sing for shit.
Though, me ma reckons that I can, and shes a singing teacher. Myahps I hold myself to too high a standard, or mayhaps shes just being nice.
I couldnt play and talk for years either. Then one day a mate asked me a quesiton when I was bashing a guitar, I answered, not thinking about playing or speaking, and did both fluently. Can do it any time now. Go figure.