rig crash after about 1 hour

[Spufa]

 just completed my rig earlier today and left it running in order to test it. I got single r9 380 (i have 2 more but i just wanted to test with single card) and i left it running and it crashed after about an hour. I booted it up again and it happened 2 more times. r9 380 is not overheating (temp about 61-2 celsius and fans set to 90%). Core clock is 820 , memory 1500. I did not touch voltage settings. I'm trying 1465 for memory now . Anyone know what else might be a problem ?
Specs:
H81 pro btc
celereon g1820
4gb ram
250gb hdd
r9 380 (single card atm)
win 10
claymore miner
15.12 drivers

I already tried switching different risers and got same problem. Reduced overclock to 1400, same. PSU was in my gaming pc for about 7 days and had no problems with it.