I tried this combination, but resukt is No post I have MB:Asus P5b-E, CPU: C2 duo E6600, PSU: Nexus 630W(82+), and I changed old gpu: GF 8600GT to Ati 5770
More about5770 compatibility asus
As long as you installed properly and connected your power supply to your 5770, you should be good to go. It is possible that you have a defective card. Is your system beeping when you power it on? What exactly is it doing?