Pink screen crash can some1 please help

OS Name Microsoft® Windows Vista™ Ultimate
Version 6.0.6000 Build 6000
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name AKHIL-PC
System Manufacturer XFX68L
System Model XFX Nforce 680i LT
System Type X86-based PC
Processor Intel(R) Pentium(R) D CPU 3.00GHz, 2999 Mhz, 2 Core(s), 2 Logical Processor(s)
BIOS Version/Date Phoenix Technologies, LTD 6.00 PG, 9/28/2007
SMBIOS Version 2.4
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "6.0.6000.16386"
User Name Akhil-PC\Akhil
Time Zone India Standard Time
Total Physical Memory 2,045.94 MB
Available Physical Memory 1.14 GB
Total Virtual Memory 4.21 GB
Available Virtual Memory 3.36 GB
Page File Space 2.29 GB
Page File C:\pagefile.sys

I have the NVIDIA 8400 GS graphics card and Zebronics 500W RED Power Supply...
For the past few days my computer has been very slow and when my graphics driver was installed it used to crash a lot specifically the pink screen crash. I uninstaled my graphics driver but still my computer is slow even after reducing my resolution and system settings to "Adjust for best performance".

CAN SOME1 PLZ HELP?