The scene in question is when Sara and Warrick go back to the Berlin house where Sara tries to start the computer. The computer won't boot because of the pistol stowed away in the case.
In reality however, it is very implausible if not completely impossible for this to prevent a computer from booting. The only possible reason for this to actually happen is if Kenny jammed the pistol inside the case with such force that it actually damaged the motherboard, or if the pistol was placed in such a way to bridge paths on the board (very unlikely considering the pistol was placed parallel to the board). Simply placing a normal object inside a computer case (i.e. doesn't produce electricity or moisture) will not prevent a computer from starting up, and at most will only restrict airflow to the point where the computer will overheat eventually.
Considering the limited amount of time that the suspect presumably had before CSI showed up, It's doubtful that he actually had the time to use the computer for any length of time after stowing the pistol.