Hello all,

I am pretty new to mining but have had decent success up until recently when I decided to add a 4th GPU to a previously rock solid mining rig. 

Here's the build:

ASRock 970 Extreme 4 Mobo
1300w Antec PSU
(4) MSI R9 290x GPUs
8GB RAM
Windows 7 Pro 64-Bit
AMD Sempron CPU

Prior to adding the 4th GPU the system was completely stable and never had an issue mining at 880kH per card.  I notice that the monitor has some flickering problems under normal use (just simple opening files on desktop).  Two of the four GPUs are on powered risers (one is a 1x to 16x and the other 16x to 16x).  Sometimes the rig will be on for 6+ hours with no problem (hashing at approx 3.5 Mhash) and sometimes it shuts down after 2 minutes.  When it shuts down it doesn't give an error message or BSOD.  It just randomly shuts down and reboots to login screen.  Please let me know if you know whats happening or can point me in the right direction.  Anyone else have similar issues?  Is the PSU not supplying enough power?  I read elsewhere that people run (4) 290's on the same Antec 1300w psu.

Any help is greatly appreciated!  This problem has been driving me nuts for the last 2 days!!

Thanks!!