Internet TV: no Picture, but Sound (1 Viewer)

[Aquarius]

TV-Server Version:
MediaPortal Version: 0.2.3RC2 + SVN
MediaPortal Skin: Blue two 16:9
Windows Version: XPSP2
CPU Type: ATHLON 2500XP
HDD: SAMSUNG Spinpoint 350GB
Memory: 512 MB CORSAIR TWINX
Motherboard: ASUS A7N8X Deluxe
Motherboard Chipset: NVIDIA 2
Motherboard Bios:
Video Card: Radeon XXL (9800 PRO)
Video Card Driver: Omega
Sound Card: onboard AC97
Sound Card AC3:
Sound Card Driver:
1. TV Card: PVR350
1. TV Card Type:
1. TV Card Driver:
2. TV Card:
2. TV Card Type:
2. TV Card Driver:
3. TV Card:
3. TV Card Type:
3. TV Card Driver:
4. TV Card:
4. TV Card Type:
4. TV Card Driver:
MPEG2 Video Codec:
MPEG2 Audio Codec:
Satelite/CableTV Provider:
HTPC Case: Silverstone LC13
Cooling: 7 fans, downnoised
Power Supply:
Remote: MCE
TV: CRT 16:9
TV - HTPC Connection: VGA-SCART

Hi all,
when selecting a Internet TV Stream , I can hear the sound, but no picture is showing up. Just a blank screen.
Does anybody have an idea, where to start searching? The logs don't show any error.

Internet TV Streams are embedded with a PLS- file in Radio section. Is that perhaps the problem ? Whereelse can I integrate PLS- files.