I have done a variation of the Tom's Budget Gaming system - I swapped for a MB GIGABYTE GA-Z68A-D3H-B3 Z68 MOBO as I am using a 60GB SSD with the Intel SRT to speed disk access.
The system will not see with the SAPPHIRE| 100314-3L HD6870 1G R that is part of this build when I boot, or on-board video. The boot seems to happen, watching the disk accessing and such - Just no video to see anything.
I checked for possible bandwidth sharing problems on the PCIe bus and it all looks cool.
The build recommended a smaller power supply than I would use but as the system is "light" with only 1 card I went with Tom's recommendation on it. (450 watts) and only an I5 processor. (no expansion plans), I did the math and I am under 450 adding it all up.
I have the drivers installed, the board is powered up, I get no unusual beep codes booting, nothing strand seems to be going on except I can see anything on video port - the 6870 or MOBO ports.
I checked at all the BIOS settings and they appear fine. I have not tried disabling the internal video in my bios, as I have an older system that has a nvida card in it with internal video and it never has a problem.
I do not have another system to put the 6870 into to check it, so that complicates debugging.
Ok. I figured it out. A couple of things. I had to do ..
1. I went into the BIOS and forced the onboard graphics to be always on
2. I booted with the 6870 in the system.
3. The previously installed AMD drivers where nowhere to be found, so I re-installed them
4. Rebooted with the video still on on-board video and I could then see the 6870 but it was not active.
5. Rebooted with video on 6870 and I am good
I hope this helps someone else having some problems.
well if you can see the bios, the video is obviously working. So that roots out the possiblity of it not being plugged in good enough. You are getting enough power to the card otherwise even the bios visual (UEFI bios or not) would have been a little laggy.