Hi, Welcome to the Forum hassankachal !
Here are all important links:
http://lmms.io/forum/viewtopic.php?f=1&t=4740
-A few rules and useful forum instructions
You write 'downloaded samples' is that also true about the many samples that comes with LMMS?My Zyn instruments are working fine,
all of my downloaded samples just aren't working.
Samples are played with either AudioFileProcessor
https://lmms.io/wiki/index.php?title=AudioFileProcessor
or Sample-track
https://lmms.io/wiki/index.php?title=Wo ... th_Samples
Firstly read those guides!
Then pay attention to the loading of the sample:
A correct loaded sample must look like left side of picture!

Try these, Let us know the outcome :)
And tell us the OS and LMMS version too, it you fail