Hardware Help!

MY computer randomly shutsdown/restarts well actually it does nither its in the middle.It shuts down but its not totalty off and it dosnt restart and its not in sleep/hibernate mode and the smell of burnt plastic/rubber comes from it.... Im afraid that if this keeps happening, somthing in my computer wilde/melt/cease to fucnction/ die a painful horrible death.... (sorry got carried away :P but you know what i mean). If anyone could help me i would be very thankful...
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System specs:
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Operating System: Microsoft Windows XP
Processor: AMD Duron(tm) @ 1.87 GHz
Graphics Card: NVIDIA GeForce FX 5200
Total Physical Memory: 768 MB
Free Physical Memory: 545.03 MB
Motherboard Manufacturer: ASUSTeK Computer INC.
Motherboard Model: A7N8X-X
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CPU:
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Manufacturer: AMD
Family: Duron(tm)
Internal Clock: 1.87 GHz
Internal Clock Maximum: 2.93 GHz
External Clock: 166 MHz
Socket Designation: Socket A
Type: <unknown>
Upgrade: ZIF Socket
Capabilities: MMX, CMov, RDTSC, 3DNow!, Extended 3DNow!, SSE
Version: AMD Athlon(tm) XP
CPUID: 0x000006a0
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Video Card:
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Description: Primary Display Driver
Manufacturer: NVIDIA
Name: NVIDIA GeForce FX 5200
Total Local Video Memory: 128 MB
Total Local Texture Memory: 128 MB
Total AGP Memory: 62 MB
Display Driver: nv4_disp.dll
Display Driver Version: 6.14.10.5216
Driver WHQL Certified: Yes
Max Texture Width : 4096
Max Texture Height: 4096
Max User Clipping Planes: 6
Max Active Hardware Lights: 8
Max Texture Blending Stages: 8
Textures In Single Pass: 8
Vertex Shader Version: 1.1
Pixel Shader Version: 1.4
Max Vertex Blend Matrices: 0
Max Texture Coordinates: 8
Vendor ID: 0x10de
Device ID: 0x0322
Sub-System ID: 0x00000000
Revision: 0xa1
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MotherBoard:
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Manufacturer: ASUSTeK Computer INC.
Model: A7N8X-X
Version: REV 2.xx
BIOS Vendor: Phoenix Technologies, LTD
BIOS Version: ASUS A7N8X-X ACPI BIOS Rev 1006
BIOS Release Date: 08/19/2003
BIOS Properties: Plug and Play, Flash, AGP