Sigardian Paladin's first ability applies as long as you put a +1/+1 counter on a permanent this turn and that permanent was a creature at the time you put the counter on. It doesn't matter if that creature later left the battlefield, lost its counters, or somehow stopped being a creature.

Sigardian Paladin's last ability can target only a creature with a +1/+1 counter on it. Once that ability has resolved, the creature has trample and lifelink until end of turn even if it somehow loses its counters or stops being a creature (although trample doesn't help a noncreature permanent much).