I believe this is a Sparkle branded Nvidia graphics card.
It got a lot of good reviews on the various web sites I looked through, also if this pdf link works, this is your video cards specifications: http://www.sparkle-usa.com/downloads/SXG210512D2-NM.pdf
You have a 450 watt power supply, the card calls for the following:
Minimum 300W or greater system power supply (with
a minimum 12V current rating of 18A)
Did this system ever boot up? If so, did the problems start after you added or changed a piece of hardware?
Have you tried different configurations on the RAM sticks? In other words, have you tried only booting with one stick (if your have more than two) at a time? Have you tried switching one stick of RAM for another?
Most importantly, make sure the motherboard is not shorting out to the system case where it is mounted, this is a common problem and is hard to see visually, try loosening the screws that hold the motherboard in place and see if the system boots.
Low profile systems do not allow for much clearance with other metal objects, including expansion card brackets, those can short out to the system board and can be very hard to see.
The system will beep if it detects a shorted circuit.