Before I ask my questions let me tell you the system I'm working with. HP, P6720F, AMD Phenom IIx4 840t, Processor 2.90Ghz, 64-Bit Operating System, Installed RAM (6.00gb) - usable RAM (5.75gb), Windows 7 Home Ed.
Q: How can I increase my processor? My computer was recently tested for work and said my processor was 1.60ghz. Why has it decreased from what was installed?
Download "CPUID CPU-Z".It will tell you what your proccessor's freq is operating at currently.
All AMD processors have AMD Kool&Quiet technology which decreases the voltages and freq while the processor is not in a power state.It is possible that what you saw was this technology working.