SN95G6 v3 - system freezes, audio shreeks

My system is a SN95G5 v3 with
Athlon 64 3500+
Mushkin DDR 1Gb x 2 (400)
2 WD 120 Gb SATA HDD
DVD R/W OEM
GeForce 6200 vid board driving a Sony SMD HS95P
all USB ports/Firewire supporting printer, WiFi, external HDD's.
Logitech speaker system
OS dual boot to either WIN 2000 Pro or Fedora 5 linux

PROBLEM: System boots, OS loads. But sooner or later the display freezes
and speakers begin a loud pulsing shrieking sound. Keyboard and mouse
input not available. System must be rebooted by button on Shuttle case.
This problem will happen early in the session or more often in the first
30 minutes of operation.
It may be a heat problem or some conflict with the video card or power
demands of the card.

System will freeze running linux too but no shrieking as I have not
gotten sound to work with linux yet.

Any similar problems?
Solutions??

M Marsh