Reseat the card, and make sure it's plugged in all the way. Then check you power cables running to the card, make sure they are secured. Reseat your ram, and then reset you CMOS. If none of the above works, try your old 9800 GTX+ and report back on the results.
I would try and get it running if I were you. If it works it'd be a major upgrade. Remember to reset CMOS. And check all you connections. The 5870 takes 2 PCI-E connectors. A 6 pin and an 8 pin. I don't know if the 9800GTX+ does or not.
It's simple, just unplug your PC, pull out the little disc battery on the Mobo and wait 15 minutes. If you tried all that and made sure the GPU sat in there correctly, I would take the computer to the person you got the card from (assuming they are local) and tell them what the problem is.
I reset the CMOS and now I can get the post message and BIOS to display. (no more no signal on the monitor)
BUT after the post, the screen flashes randomly colored pixels 3 times and then just goes black (does not display no signals).
SO I'm still stuck with a black monitor after the bios post.
Thanks already for your help but I need a little more to get there I fear!
I reset the CMOS.
1. Now BIOS displays
2. After inital post/bios message, screen flashes 3 times (random pixels, black, random pixels, black, random pixels, black)
3. Then it just stays black although the fans and HD start spinning up.
I really don't think it would help much, a good 650W should be more then enough. If you have easy access to a 800W PSU, you could try it. Maybe the 5870 is even more of a hog then I though thought. I guess it depends on what else is in your PC?