low hash rate

Hello,

I have a problem with 7990 card My setup:
- Intel celeron 1820
- mobo asrock h81
- 1200W PSU (Platinum)
- 8GB RAM
- 160GB SSD
- windwos 10
- 1x to 16x powered risers

the problem is my 7990 only give me 24MHS

it most give me 40MHS or more

driver version : 16.300.2311

what i can do ?????