Notebook Is Slow While Connected To HDMI?

today my notebook asus m50vn suddenly started to behave weird. while it's connected to plasma via hdmi, everything starts to stutter a bit, which is very inconvenient in videos.it works like this: 0,5 s of fluid picture, 0,1 s of freeze, 0,5 s of fluid picture, and so on.situation is the same on primary (built-in) monitor and secondary (plasma), as well as on Internet, vlc, potplayer and mpc hc. dxva and cuda won't make any difference, choosing different video renders in player's settings won't do ve already tried to install older and newer drivers (graphics is geforce 9650m gt) computer is 100 % virus free, there is comodo is for on-access security and i've also checked it with malwarebytes, hitman pro, emsisoft emergency kit, kaspersky tdss killer and cce. almost all processes are disabled.it's interesting because there's no problems when plasma is connected via vga.