CPU speed stuck

I'm using Dell Inspiron 15R N5110, which has Intel Core I7 2630QM. I recently installed Windows 7 SP1, uninstalling Windows 10. I ran Windows Experience Index and CPU-Z,

and my CPU rating is decreased to 4.5 (previously 7 or above). I checked CPU-Z showing the CPU running at a low speed.At task manager resource monitor in windows 8.1 it show CPU speed always at 0.76 GHz and remains same even if I load CPU heavily up to 100% .

But I also checked in Safe Mode it Worked fine there and CPU speed goes above 0.76 GHz and even to Turbo as well. But I can't figure out what is the problem in Normal Mode where CPU always runs at 0.76 GHz. How to figure out what's going on. I also diagnosed CPU by Intel Processor Diagnostic Tool  and it passed everything. How can this be fixed.???