Can any one know why 4 GPUs working out of 5 GPUs

Hi,

I am new to the mining and have an issue which I need to ask you experts. My rig has following stuff on it:

1. Gigabyte 970A-DS3P
2. 8 GB DDR3 RAM
3. AMD FX(TM) - 6300 Six - Core Processor
4. 120 GB SSD
5. Corsair 1200 W Platinum PSU
6. 4 GPUs are Gigabyte RX-470 and 5th card is MSI RX-480
7. Fixable PCI-E 16X to 1X Adapter USB3.0 USB 3.0 Riser Cable Flex Flexible Extension Cable w/ Molex 4 Pin Power Connector
8. Windows 10

I am running Claymore's Dual ETH + DCR/SC/LBC/PASC GPU Miner v9.4. Also I have 6 GPU MOD which has been run.

Now when I run 4 GPUs, they run fine. But when I try to run the 5th GPU I get this msg " EthDcrMiner64.exe has stopped working" (without the exclamation marks).
Can anyone plz help.