all,heres my situation,i updated my little girls acer aspire m3400 to a saphhire hd5770 at the same time i upgraded the psu to a 750watt model and that has worked fine for a few months,so i upgraded my sons and was left over with a sapphire hd6870 which i thought i would just install in my daughters and that wud b that,it wouldnt boot(gets to windows post screen and freezes),no problem i thought must be the ati ccc drivers so i reinstalled the hd5770 with the intention of dloading the ccc drivers,no joy now that card wont boot,so i thought it must be something to do with onboard graphics,theres a hdmi+vga port on the mboard so i took out the gcard altogether and connected to the hdmi port on mboard(i havnt got a vga cable)and that wont boot either,i've reset the cmos with the jumper to see if that works,still no joy,so i made a usb bios flash drive with the latest bios for that model of comp from acer,that went ok,no probs,but still wont boot with 1st onboard 2nd hd5770 3rd hd6870,i can get into bios and thats about it,i've tried to start rinstalling windows but as soon as the windows logo starts to appear(the bit where the dots spin round)it just freezes,any ideas anyone,i've got a funny feeling the mboard couldnt take the increased power draw for a hd6870 and i may have fried it,ps i cant get into safe mode i've tried all the keys but i dont know which one to hit,any ideas anyone.thx 4 any help....just checked,i've being running memtest since 2.30am and no problems with the memory,finally found the safe mode(f8) button but still freezes/goes greyed out as soon as it tries to load the windows logo,it displays bios type text,but not even basic grphics text at all.ps bios says hdd smart health ok and everything is default settings and yes it was unplugged when i swapped the cards ect
On the 6870 you have a 6 pin connecter from the PSU. Did you connect that 6 pin connecter to the back side of the 6870? Now I need to see all of your specs on that PC including the PSU brand and wattage.
One thing you don't have to worry if there was not enough power to run the card. If that was the case you would never get it to boot. So you didn't burn the MOBO out.
You also should have a VGA or a DVI cord to test with. Get back to us with the info and we will try to help you out.