Core i7 -5500u stuck at 499mhz clock speed [duplicate]

You CPU is running in idle mode, which is multiplier 8 : 800 MHZ = 100 * 8. The CPU-Z report shows that its is capable of reaching up to a 34 multiplier, which is 3400 MHZ, and HWINFO says the same.

As a first test, you could run the Intel® Processor Diagnostic Tool, although I don't really expect it to find anything.

Second, have you opened your computer lately? There a switch on the motherboard which tell the CPU to always run at the lowest speed. This switch is called Slow mode or LN2 Slow Mode or OC Trigger Switch (TGR) or else. You might find its description in your motherboard's manual. It is sometimes situated right next to the power reset button. Even if it on the right position, sometimes just moving it between positions corrects the problem.

There might also be BIOS settings that disable the CPU thermal monitoring if it became defective. These might be called EIST and/or Intel Adaptive Thermal Monitor. If this helps then something is wrong with your motherboard.

Another such setting is BD PROCHOT (Bi-directional Processor Hot), an emergency throttling system that is used when a CPU hits its maximum temperature. To disable it temporarily, download ThrottleStop to check on and disable BD PROCHOT. ThrottleStop when running can also correct several types of CPU throttling. Again, if this helps then something is wrong with your motherboard.