Oh darn - HELP!

[Mitchamitri]

Couple of weeks ago kegged off a beer kit (a Youngs one) as the g had got down low enough and stabilised so it was ready to keg. Primed it with the right amount of sugar. made the elementary mistake of leaving it in a fairly warm place for a couple of days but obviously not for long enough as a sample taster last night it was very sweet - too sweet - judging by the lack of fizz but lots of froth so the secondary hasnt started correctly. After the couple of days I moved it into my garage which is basically outside temperatures.
Its in a keg - do i just move it to a warm place and let it restart? Should I put some yeast in? SHould I leave it sealed or let the C02 out? Can it be rescued?