Ubuntu 11.04 Natty, upgraded from 10.10

Hello, I usually use VLC player to play my videos because I have poor speakers (VLC can multiply the volume by 400%). Unfortunately, ever since I upgraded to Natty, when playing any video (especially FLV files) on VLC, suddenly out of the blue the sound stops, the frames speed up and the system begins slowing down. If I don't quit VLC immediately (the quitting itself takes too long once the problem starts) the cursor stops responding and the system remains frozen.

Tried this on my Athlon x2, and sometimes it happens, sometimes doesn't. All I know is that I managed to replicate this bug: even my netbook had Maverick, which I then upgraded to Natty, and the same video problems persist there.

Could I get some advice on this, please?