- To check on resources, download the free Sysinternals suite from Microsoft (http://technet.microsoft.com/en-US/sysinternals) and use Process Explorer. You can add columns to show memory use ("Private Bytes") and processor history per-process.
- Try moving the audio card to a different slot if possible.
- Which VNC are you using? I would recommend RealVNC, as it is very mature and stable in production with no known memory leaks. I've had issues in the past with UltraVNC and the like.
- Re-seat the RAM.
If the site is dirty or dusty, that will cause issues with RAM and peripheral cards needing removal and re-seating on a regular basis too.