Hello all,
Got a HD4780x2 off one of the lads (SeantheMan), but when I put it into my machine, I only get a black screen. It worked fine for him, but he's since updated to two HD6870's so he gave me the HD4870x2.

When I boot, nothing comes on the screen, and the fan stays at full power. If I leave it alone, I can hear the Windows chime after about four minutes, so it seems it works, but just gives no output. Have tried both DVI ports, and have also taken it apart and cleaned the dust & cleaned and put new paste on the heatsinks, but still no joy. Have the 6pin and 8pin power conections hooked up to my 850W CoolerMaster, so there should be enough juice.

Anyone have any ideas? I can't install both cards at the same time, as there's not enough room.

first thing you should do is put back your old card to see if the machine will post and have graphics.

Done, and using it at the mo.

if it does then you know the problem is with the new card.

Yup.

Try reseating your cpu as you could have easily knocked agiainst it while installing that big motherfucker card.

Didn't go near the CPU; when changing parts, I have the case flat on it's side to prevent such happenings. Would prefer not having to take off the TRUE120 heatsink (the fan is annoying to get back on) to reseat the CPU, and as it's bolted on so well down I doubt it would've moved much.

when changing hardware in machines especially graphic cards..dimm memory can be a big problem,try reseating your memory,or changing dimm slots

Have reseated the DIMMs, but didn't change the DIMM slots (currently in 1 & 3). Will try that at the weekend. Also removed the CMOS battery, booted it, shut it down, and put the CMOS battery back in to clear the settings, but it made no deifference.

your not running a asus rampage 2 exteme motherboard by any chance are you?

No. It's a Gigabyte GA-X48-DS5 motherboard. May update the BIOS, as F8C is no longer a beta version.

is the card damaged in anyway? any cracks or chips in the PCI slot?

Can't see any damage, no.

Took out the soundcard, rejigged how I put the fan onto the 4870, and I got both cards into the PC. It runs, but still no display from the 4870x2. I have the crossfire cable connecting them both.

In fact, the PC doesn't seem to see the 4870x2 at all, either in Device Manager, in CPU-Z, GPU-Z or in MSI Afterburner.