For a media-center I recently bought an AMD Club3D HD 5450 with 512mb ddr2 ram, and i have installed it in an asrock M3A770DE motherboard.
But i keep having an issue with it, it performs really bad, and cant even run windows aero properly.
Now I have to admit that my PSU does not fulfill the demands of a 24-pins and a 8-pins power connector(it provides a 20-pins and a 4-pins instead).
Also, the card uses a PCI express 2.1 slot, and the motherboard only supports 2.0, but since it should be backwards compatible, this should not be a problem.
I have of course updated the drivers and have searched for an answer elsewhere.
Overclocking only made it unstable and made itself restart every 5 minutes. The card is passively cooled.
While a new (modern PSU) certainly wouldn't hurt. It really has nothing to do with the performance issue described by the OP. If the PSU weren't up to the task, the GPU wouldn't work at all or the system would constantly crash.
First off, you should not OC the 5450 at all. It really isn't designed to handle that and the passive heatsink is definitely not up to the task. The 5450 can actuallu get quite hot when under load if you don't have good airflow and temperature control in your system. That will definitely lead to poor performance (your OCing comment indicates a heat problem).
How are you CPU and GPU temperatures at idle and under load? If you don't know, get hwmonitor and run in the background while playing a video.
Yes i have checked the temperatures of both the CPU and GPU. When they were at factory settings an idling, the temps stayed under 45 degrees celsius, and if active, they were like 60 degrees. No much difference when (slightly) OC'ed around 65 degrees GPU and my CPU stayed at 55 degrees at 4 gHz (amd athlon x2 250)
so I thought the temperature couldn't be the reason for it to restart itself..