That symptom could have a non-malicious cause, try this first:

* Open the Event Viewer utility in your Administrative Tools control panel and look through your System and Application logs for entries flagged with "Error" or "Warning", especially
those which mention the "Explorer.exe" program, or whose time-stamps coincide with the occurrences of the problem.

* Double-clicking on such an entry will open a properties window with more detailed information on the error; post the details from a representative sample of some of the different error messages (please don't post duplicates of a given entry, or flood us with the entire contents of the logs).

* To post the details:
In the Properties window of a given entry, click on the button with the graphic of two pieces of paper on it; the button is at the right of the window just below the up arrow/down arrow
buttons. You won't see anything happen when you click the button, but it will copy all of the details to the Windows clipboard. You can then paste the details into your next post here.