With the PC market flagging in general at the moment due to tablet sales disrupting what was once a reliable PC upgrade cycle, many Microsoft (NASDAQ:MSFT) investors were hoping that the company's new operating system, Windows 8, would rekindle consumer interest and drive a lot of PC sales. However, consumer market research group NPD recently released a study saying that Microsoft-based PC sales were down by more than 20% over the last month. In this video, Motley Fool analyst Andrew Tonner talks about why this could be a real red flag for Microsoft investors, and may affect the investing thesis in the company. He also highlights some potential margins for error in the study itself.

Andrew Tonner owns shares of Apple. The Motley Fool owns shares of Apple, Google, Intel, and Microsoft. Motley Fool newsletter services recommend Apple, Google, Intel, and Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.