Common Issues with Sparkle Power FSP300-60BT - Sparkle Power FSP300-60BT (FSP300-60BT)) 300-Watt Power Supply

It's not worth enough to warrant you risking your life to replace it. Especially on that piece of garbage PSU. You can die if you try fixing a power supply and touch the wrong thing inside. Seriously.

if you go into the bios setup you can check the power supply volts there to see if there preforming correctly that and check the cpu heat in the same place

In that case the graphics card that u have mentioned might be faulty. Try downloading the latest the update for the graphics card from the manufacturer's website and check. If the same issue remains then the graphics card is faulty.

have you connect the external powersuplly to the card?

if the power supply has the 6 pin connector to plug into the video card, you should have no problem using this card with your current setup..
i currently use a GeForce 9800GTX+ with about the same pc as you have using a 600w power supply and no issues what so ever, generally the video card power supply requirements will be stated on the side, but i'm pretty but it requires a 450w or 500w, so you should be fine.

Sir,
To me it seem the Driver setting of Card or the power managment problem of you Computer. You are suggested to click on control panel and there go on to power management then do all the Power options to "NEVER" option in them. this might fix your problem

Did you make sure you uninstalled the original 9600gt driver, other than that you could try safe mode with networking and download/install the driver.

You need to locate the PS_ON pin and short to ground (GND). This pin may vary depending on model and I don't know if green is the standard color for this, but it is green on the unit I just looked at for reference and it it aso shown here http://pinouts.ru/Power/atx_v2_pinout.shtml
any black wire should be ground

I suspect that your power supply may have overheated if its fan is not working properly try another power supply

Go to this site: http://pinouts.ru/pin_Power.shtml.

It should have the pinout info you need. If you're intending to fix the unit, you can get a replacement (with more power) at this site for less than $20, including shipping: http://www.geeks.com/.