I just realize that the speaker icon on the taskbar is gone and that i can't use PrtSc anymore. I don't know what happen, if you have any clues about how to fix that i'll be a happy man
Are you running KDE?
In that case I take it that the speaker icon has disappeared from the system tray on the panel. This is probably because Kmix has crashed, so first of all try restarting Kmix from the menu. (It could also be because the settings of either Kmix or the system tray has somehow become corrupted but we can get to that if just restarting Kmix doesn't help.)
If you used to have a speaker icon outside
of the system tray, you could recreate it the normal way. (Unlock widgets, rightclick Kmix in menu, add to panel.)Added:
If you are running KDE the shortcuts involving PrtScrn are set in "Configure Your Desktop"->"Computer Administration"->"Keyboard & Mouse"->"Global Keyboard Shortcuts"->"khotkeys" and "KWin". (But PrtScrn does double duty as the SysRq key.)
If you aren't running KDE, tell us which DE you are actually using.