Try to increase size of physical RAM, for 4 290 cards at least 4GB is necessary, 5 cards may require even more. You can also try to increase size of virtual memory.
I came home to the rig only showing 4 cards and the 5th's fan spinning at 100%. moved the 5th card in to a different pci slot, increased virtual mem to 18GB:
5x Sapphire R9 290 Tri X @ 1000/1250
Speed: 3731 h/s, TotalHashes: 503585K, DevHashes: 12588K Mining time: 38:14
10:07:25:440 99c GPU 0: HashCnt = 1280, time = 1698 ms, hashrate = 753 h/s
10:07:25:480 99c Round
10:07:25:880 594 GPU 4: HashCnt = 1280, time = 1702 ms, hashrate = 752 h/s
10:07:25:905 594 Round
10:07:26:035 eb0 GPU 1: HashCnt = 1280, time = 1697 ms, hashrate = 754 h/s
10:07:26:070 eb0 Round
10:07:26:100 890 GPU 3: HashCnt = 1280, time = 1696 ms, hashrate = 754 h/s
10:07:26:115 890 Round
10:07:26:705 77c GPU 2: HashCnt = 1280, time = 1746 ms, hashrate = 733 h/s
10:07:26:740 77c Round
Looking good.