Remove all your old graphics drivers and run driver cleaner....
Then reboot and install the latest ATI drivers.....with or withopu the ccc.
Also you might have a contact problem so clean the PCI-e slot with an aproved cleaner and re-seat.
Hope this helps....JQ
Driver problems would not likely cause your system to just power off. You have a Chokemax PSU. It is not capable of [reliably] powering your system with that GPU. That a few others may have worked can be attributed to luck.
Replace it with a quality model of 500W-550W. Look for one with full range active PFC (no little voltage switch) and 80+ certification. Antec, Corsair, PC Power & Cooling, Seasonic, and Enermax are among the better brands.