A:
It could be one of a few things, depending on how long you've had the computer.
Its possible you have a virus on the system that causes this. In that case, I would suggest backing up all the information you want to keep to a flash drive or a cloud storage account, and then refreshing the machine. You can do this by going to the Charms bar (move mouse pointer to top left of screen to open the bar), select Settings at the bottom of the bar. This will take you to the Windows 8 settings. This is different from the Control Panel in that all these things are specific to Windows 8 and your personalization of the computer. There will be a tab that says "Update and Recovery", select that and then select the "Recovery" tab. From there, you can choose 2 of the 3 options. You can refresh the system, which will essentially reset the PC to factory settings, but save all your files. This might work, but if the error is caused by a virus, this likely will not work. The other option is "Remove everything and reinstall Windows". This will erase everything on the computer, and reinstall the Windows operating system, essentially giving you a new computer. If you have a virus and you cannot remove it with an Antivirus program (Windows Defender is free, comes already on the computer and set up, just search for it from the Search box in the Charms bar and select the full scan), then you'll want to do this to save the computer.
If its not a virus, its likely a setting you have set on the computer or something similar. You can simply refresh the system as I described above and that should fix the issue.
If its a hardware issue, such as one of the processor cores malfunctioning or an error with the RAM, you should take the PC to Best Buy for repair or replacement. They can transfer all your information from your broken computer to a new one, and you can be essentially back where you were with the old computer with a new one, only the new one will work properly