1050MHz is too high for this GPU. 900 MHz is a max safe frequency
1.Uninstall any software for GPU and system tweaking
2.Delete C:\AMD folder
3.Uninstall all AMD software and clean your system in safe mode by DDU program and install 15.7.1 or 16.2.1 driver
Thanks Redfury, all sorted now. It runs stable at 970MHZ with memory at 1450 and voltage at 10% ;fan is set to 60%.
I found a pair of Sapphire HD 7990's one kind of works and one works.