Processor Speed Limited to 0.79GHz / 800MHz

One of the possibilities for slow performance issues maybe caused by the processor speed being limited due to processor throttling, also known as processor dynamic scaling. The processor might use this feature to descrease its speed to save power or reduce the amount of heat being generated.
There are several reasons that could lead a processor to use this feature as for example Idle time (save power) and high temperatures (cooling system).
As the processor speed is controlled by the motherboard and chipset, there might be some rare scenarios where the processor get stuck in in lower speeds and is not able to recover from this status.

In order to reset the throttling flag set on the processor by the BIOS/Windows system, it would be necessary to perform a RTC Reset.
For portable systems, you can perform a RTC Reset by following the steps described in the article How to Reset Real Time Clock (RTC) to recover your Dell Portable system

On a desktop or workstation, the fastest way to perform this it to remove the CMOS battery and hold the power button for 15 seconds. After reconnecting it back to the system you can check if the processor speed is now unlocked again.

If these steps do not correct the issue, please contact Dell Technical Support.