The modded bios on this site is exactly the same as the original only with SLIC 2.x added so one can use Windows pre-activation technologies... with other words: no it won't solve your problems
RMA your card. This happens on my 4870X2 if one of the power connectors isn't connected. Fans run at 100% and the system won't post, and the lights on the card blink red.
Be certain you have an adequate power supply and the external power connectors are plugged into the video card before attempting to turn the system on. One thing to try is to remove all other pci/pcie cards and see if it posts. The 5770 either cannot get enough current to initialize or there is a hardware compatibility issue I am betting. Is there a newer BIOS for the motherboard that might address such an issue? You have classic symptom of inadequate power supply for the cards needs. Some older PCIe 1.0 based motherboards do not play well with PCIe 2.0 cards, specially high current draw cards. I see from google search you are not alone with a HD5770 that won't post.
Guys he said this: Personally I haven't checked but yea you should return the card and get it replaced for another model.
Thanks for replying! I think it is incompatible en that the scale of mobo's that are incompatible is too small to be mentioned on the system requirements. I tested the card in another system with my own PSU, and it worked great! So i'm going to buy me a new mobo with a nice PCIe 1.1 or 2.0 slot, because this incompatibility only seems to happen with mobo's that have PCIe 1.0. But anyway thanks for thinking with me. May Holland win the worldcup!