I have a k2000 and usse all the outputs, but i can't hear the effects.

I'm not sure about the K2k but with the K25, the internal fx only comes out of the "MIX" outs and by using the outs labeled as "A" pair, you bypass the internal fx.
On the programs "output" page, you determine which pair of outs will be used and the options are listed as; A(FX), B(dry), C(dry), D(dry).
On my K25, I use: MIX, B, C, and D outputs and leave the pair labeled "A" unplugged.

Also make sure Effects mode is set to Auto or Program