Screen gets lines and flickers

Hello,

I have recently gotten a horizontal line across my screen it makes the bottom half of the screen shake up and down, I've already checked my device manager and Dxdiag and both say the graphics card is fine. The line disappears completely when I launch one of my games with no problems at all (the screen also stops flickering). Any help would be greatly appreciated.

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Time of this report: 8/12/2012, 17:59:33
Machine name: QUADZILLA
Operating System: Windows Vista™ Ultimate (6.0, Build 6002) Service Pack 2 (6002.vistasp2_gdr.120402-0336)
Language: English (Regional Setting: English)
System Manufacturer: System manufacturer
System Model: P5K Premium
BIOS: BIOS Date: 06/26/07 14:33:14 Ver: 08.00.12
Processor: Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz (4 CPUs), ~2.4GHz
Memory: 4094MB RAM
Page File: 2746MB used, 5653MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
DX Setup Parameters: Not found
DxDiag Version: 7.00.6002.18107 64bit Unicode

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Card name: NVIDIA GeForce 9500 GT
Manufacturer: NVIDIA
Chip type: GeForce 9500 GT
DAC type: Integrated RAMDAC
Device Key: Enum\PCI\VEN_10DE&DEV_0640&SUBSYS_064810DE&REV_A1
Display Memory: 2797 MB
Dedicated Memory: 1005 MB
Shared Memory: 1791 MB
Current Mode: 1280 x 1024 (32 bit) (60Hz)
Monitor: Dell SP2008WFP(Digital)