I install new windows and hashrate was 720, then i manipulate cg miner settings and hashrate Hardly was 640, then i change settings to original settings, but i cant get first hashrate (720).
The possibility exists that Re install new Windows can get first hashrate (720)?

msi R9 280
Win7 - 64
8gb RAM
Cpu sempron 145
Driver 13.11
Afterburner The latest version