Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
What you describe is called an 'explorer crash'. There is a process called 'explorer' (not to be confused with Internet Explorer, but named with a confusing similarity.) It directs and produces the Taskbar and the Start button functions. When it crashes, they disappear - sometimes the Desktop icons also re-display in a flash.
'explorer crashes' generally indicate either an overloaded CPU, or more often, an infection by malware, and sometimes, spontaneous corruption of the operating system, or CPU or memory hardware in your PC that are a bit unreliable and erratic.
That's a large assortment of possible causes. It can be dealt with by a thorough assessment of your machine. Would you like to proceed with that ?
Is there any other advice or help I can offer you? (aside from my diagnosis of an explorer crash event, from your description.)
If not, please rate my answer, and thanks for asking your question today.