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 youtube, VLC, PotPlayer and MPC HC. DXVA and CUDA won't make any difference, choosing different video renders in player's settings won't do the help as well. I've already tried to install older and newer drivers (graphics is Geforce 9650m GT) but it didn't help.

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.

Unfortunately there's no useful system restore points.

Does anybody have any idea what could be wrong? Thanks in advance.

I don't really know much about HDMI, never used it myself yet...but this sounds a lot like the HDMI interface is simply overloaded and there's too much data to transfer it all in realtime through HDMI. I can only guess though.

VGA wouldn't have that issue since it's an analog interface, not digital - the digital-to-analog conversion is done by the onboard video itself (actually, its built-in RAMDAC).

Possibly a recent update is causing this problem. It might be worth taking a look at the HDMI device in Device Manager.

HDMI was working fine, even 1080p could be played smoothly until yesterday. Resolution of plasma is already set to 1024x768 px so that shouldn't be the issue.

It doesn't matter if I turn off laptop's screen and set projector only. Even if I turn off secondary screen and use laptop's only, while HDMI is connected, it will work slow.

Windows power options are set to high performance, there's no difference when laptop is plugged in or running only with battery power. CPU frequency is on 100 % according to AIDA64.