On the start menu task bar the open windows doesn't appear to me to navigate easily between pages I need to make it appear again

What do you mean by "open windows"?

I mean that when I open as an example my computer icon it doesn't appear on the task bar as it used to do before

Is the taskbar locked? Do you have an open bar that is empty but takes up all the space?

Use Google and search "missing taskbar buttons". You should find a fix in one of the thousands of hits.:)