SONY BRAVIA KDL 50W828 - video stuttering

Hi, I have a brand new Sony Bravia KDL 50W828, along with a not-so-new desktop PC running Windows XP service pack 3, AMD Phenom 9500 quad core 2.21 Ghz and 3 GB RAM, wi-fi connected.
At first it all seemed to be working, the TV read correctly all the files shared, but when I try to see a .mkv file with external subtitles .srt the video begin stuttering and it's nearly impossible to properly enjoy the view...
What do you think the problem is? The PC is too old? The wi-fi connection is not strong enough? Or I just set Serviio wrong?
Please help me!!
At first it all seemed to be working, the TV read correctly all the files shared, but when I try to see a .mkv file with external subtitles .srt the video begin stuttering and it's nearly impossible to properly enjoy the view...
What do you think the problem is? The PC is too old? The wi-fi connection is not strong enough? Or I just set Serviio wrong?
Please help me!!