Playing base sample once

[Skyluke]

Hello all! I've a little problem: i have a simple VST host that let me change instruments while playing, but i need to start a long sample (actually bass and drum on a wav file) when i press a certain key on my keyboard.. I've tried Kontakt, but every time i press that key, it plays a new instance of the wave file... is there any other way?

Thaaanks!!
Skyluke