|Under the heading "Specs" all you list is Windows7.|
Apart from that all we know is you have an 8400GS graphics card. We don't even know which OEM made the card.
"Some of my friends said to upgrade my power supply"
What are the specs of the existing powersupply? What motherboard? What CPU?
What and how much RAM? Which version of Win7 ? How many hard drives?
Which version of the graphics drivers are you having problems with?
Have you checked system temperatures? An overheating GPU can give the kind of symptoms you describe. Does your graphics card have active or passive cooling? If it has a fan is it working and have you cleaned it?
Goin' Fishin' (Some day)