1999 Ford KA bizarre noise when key turned - battery dead

Got into car this morning, turned key, as normal, but no action apart from a very fast and loud clicking or ticking noise. No battery reaction, at all. Friend towed me down road with car in 2nd and with clutch movement, engine fired. Seemed fine but within 30 mins was back to the clicking noise. Battery definitely dead but could the noise be a bad starter motor? Only had car a few months and it is a heap but I have not had any starting problems. Levels all seem fine. Windows sometimes don't work which might be indicative of dodgy wiring. Battery charging now. Should I wait to see if that does anything? Any advice gratefully received.