Windows 8.1 and BAMT not recognising R9 280x

[alphacenturion]

So my rig is up and running on Windows 8.1 with 3 of my MSI R9 280x cards found but the 4th is nowhere to be seen.

I have tried:

1. Various versions of Catalyst Control Center
2. Switching PCI-e slots - 3,4 and 6 are found (all 1x 16)
3. Uninstalled drivers/catalyst CC (Drivers get automatically found as soon as I reboot but only for 3 cards)
4. All cards have been tried in each slot (ie. confirmed all cards are working and spinning)
5. Tried without the molex connected on the problem card
6. Confirmed all USB PCI-e risers are working
7. Tried BAMT - same issue.

My setup is:

Asrock H81 BTC Pro mobo
8gb ram
1250w Seasonic Gold
4x USB Powered Risers

Im wondering if I need to undervolt the 3 seen cards first as Im running the PSU close to the limit at stock? If so what is the best way?

Any other ideas to get this working at optimum?

[alphacenturion]

Also Ive updated to the latest mobo bios and tried Auto and Gen2?

[alphacenturion]

Guys - I'm thinking this may be a power issue and that I need another PSU? Is this the correct thinking? Or would the card fans not be spinning at all if this was the case? Any help appreciated.

[rmines]

Have you tried undervolting the cards, will the 4th card then get recognized?

[gnomegawd]

again this is an easy troubleshoot, already have a few ideas about why you are experiencing anomalies. 

You have verified that each card works independently?  If that is already done yes, easy fix.

[dloganbill]

With that board, some are recommending to not use the powered part of the riser.  Instead use the 4 pin connections on the board.  Check out the latest Bits Be Trippin' video on Youtube for a little more depth on a similar build.

[dloganbill]

Link to BBT EP 10. These guys do pretty nice work.
http://youtu.be/WfqfEpanpig

[alphacenturion]

Link to BBT EP 10. These guys do pretty nice work.
http://youtu.be/WfqfEpanpig

Will check it out thanks.

Have you tried undervolting the cards, will the 4th card then get recognized?

Not yet but I shall try that - is it best through afterburner or something else?

again this is an easy troubleshoot, already have a few ideas about why you are experiencing anomalies.  

You have verified that each card works independently?  If that is already done yes, easy fix.

Verified yes. Easy fix probably!

[alphacenturion]

Ive discovered that one of the usb riser's usb cable isn't working properly. I've ordered another cable and will attempt to use that! Thanks for your help - its always the most simple of solutions!

[rmines]

I hope the new cable will fix your problem, thanks for keeping us updated.