community, i have one big problem.. i run windows 7 Home Premium 64 bit on a MSI Z97 G7 (Gaming series), an i5 4690k, 8 gb RAM Kingston 1600mhz, a 850watt PSU and 6 evga 750ti ACX FTW.. until yesterday i've ran my rig only with 5 cards 'cause i had only 4 PCI-e risers.. and all ran fine..today ebay delivers me the missing riser, so i've push it into the PCI-e and i've attached the 6th vga card.. now ccminer don't work.. it runs only for 30-40seconds and then crash.. i don't understand why.. with 5 card it works, with 6 cards it doesn't work..
risers aren't usb risers, they are classic riser.. i've one card attached into MoBo into the 16pin PCI-e, 2 cards attached with 16pin to 16pin risers (obvioulsy into 16pin PCI-e) and in the end the other 3 cards are attached with 1pin to 16pin risers.. what's my problem? it's caused by my rig or the problem may be ccminer? have sense to try with ubuntu?

many thanks for your attention..