NVIDIA 7300GS Problems

this is my first post to the forumz, although Ive been reading them for some years. I hope I dont sound totally ignorant but I have a problem with my GPU. It seens that when my computer has been on for some time with no activity, the screensaver set to pictures, fades to black/white, then eventually all I get is garbage. It appears to lose some of the colors and the screen (19" Optima widescreen LCD) goes wierd..
I have had it into the shop for Warranty repairs, but they seem to think its a software problem.. the Newest Drivers have been downloaded and installed from NVIDIA.

my configuation is:

Windows Vista (Home Premium)

Motherboard
Manufacturer Foxconn
Model 945 7MD Series

Chipset
Chipset Model 945G Processor to I/O Controller
South Bridge 82801GB/GR (ICH7 Family) LPC Interface Controller
SMBus Intel Corporation 82801G (ICH7 Family) SMBus Controller @0500h

CPU
Cpu Socket LGA775 [Socket 775]
Max CPU Speed 4000 MHz
One Physical Processor / 2 Cores / 2 Logical Processors / 64 bits
GenuineIntel
Intel Core 2 Duo E6400 @ 2.13GHz

Memory
2X 1024 Mb
Memory Type DDR2 SDRAM
Speed DDR2-533 (266 MHz)
Data Width 64 bits

Hard Drive
Western Digital WDC WD3200JS-00PDB0 320 GBytes SATA-II

Graphics Card
256 MBytes
NVIDIA GeForce 7300 GS

I purchased it from OPTIMA. It is not OC'd and I am not a gamer. I just need a reliable video card that I can do some Video Processing. I would apprecate some help. Is it the card? Can you suggest a more reliable card that is in the same price range? Thanks for looking at this, and Please no giggles.. Im not a computer wiz. 8O