My 27" Mid 2011 iMac with latest El Capitan beta blacks out after a few seconds. I dont know what else to do. I noticed it since 1st beta but it was never this bad. I was able to press the power button to put it to sleep then waking it back up and it would go on for a while before the problem comes back but now no matter what i do it blacks out after 30 or so seconds later. Its completely fine however on my external display, my imac is blacked out but external still shows its on and working. It went into Kernel panic two weeks ago and I got was able to fix it through safe boot but now even in safe boot the screen goes black after few seconds.
I saw another thread on here about a simmilar issue (https://forums.developer.apple.com/message/43888#43888)
and followed the advice but I dont know what to do next.
Here's some of the details I have so far if anyone could help me out.
Nick-Zipagans-iMac:~ nickzipagan$ ls -1 /Library/Extensions/
ACS6x.kext
ATTOCelerityFC8.kext
ATTOExpressSASHBA2.kext
ATTOExpressSASRAID2.kext
ArcMSR.kext
BJUSBLoad.kext
CIJUSBLoad.kext
CalDigitHDProDrv.kext
EPSONUSBPrintClass.kext
FTDIKext.kext
HighPointIOP.kext
HighPointRR.kext
LittleSnitch.kext
PromiseSTEX.kext
SiLabsUSBDriver64.kext
SoftRAID.kext
Wacom Tablet.kext
Nick-Zipagans-iMac:~ nickzipagan$ ls -1 /Library/Application\ Support/VirtualBox/
ls: /Library/Application Support/VirtualBox/: No such file or directory
Nick-Zipagans-iMac:~ nickzipagan$ find /System/Library/Extensions -name "*.kext" -ctime +11w
Nick-Zipagans-iMac:~ nickzipagan$