Hello, My computes is HP Pavilion 061 Model PX192AV-ABA m7100e.
Windows XP Pro. AMD Athlon 64 3500+ operating 2.2 GHZ
Power supply 400W max. A8AE-LE motherboard
OK. My Graphic card died (NVIDIA GeForce 6600 256 MB PCI Express Video Card w/DVI & S-Video)
I need to replace with graphic card with better card.
I bought HD 5450 silent, but isn't working.
You have an older system that is using PCI Express 1.0. Some of those boards have issues running PCI-E 2.1 cards like the 5450. You can try looking on HP's website for a BIOS update for your particular computer that addresses this issue. If there is no BIOS update you'll have to return the 5450 and look for a PCI-E 2.0 card, which on the AMD side go up to the HD 4000 series. Nvidia kept up 2.0 support a little longer, I think up to their 400 series Nvidia cards are PCI-E 2.0.
It is also possible that you got a bad card, if you have another computer, preferably a more modern system, try out the 5450 in that. If it doesn't work on another system it's probably just dead on arrival.